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Date  Due 


THE  UNIVERSITY  OF  CHICAGO 
SCIENCE  SERIES 


Editorial  Committee 

ELIAKIM  HASTINGS  MOORE,  Chairman 

JOHN  MERLE  COULTER 

PRESTON  KYES 


THE  UNIVERSITY  OF  CHICAGO 
SCIENCE  SERIES,  established  by  the 
Trusteesof  the  University,  owes  its  origin 
to  a  behef  that  there  should  be  a  medium  of 
publication  occupying  a  position  between  the 
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the  elaborate  treatises  which  attempt  to  cover 
several  or  all  aspects  of  a  wide  field.  The 
volumes  of  the  series  will  differ  from  the  dis- 
cussions generally  appearing  in  technical  jour- 
nals in  that  they  will  present  the  complete  re- 
sults of  an  experiment  or  series  of  investigations 
which  previously  have  appeared  only  in  scat- 
tered articles,  if  published  at  all.  On  the 
other  hand,  they  will  differ  from  detailed 
treatises  by  confining  themselves  to  specific 
problems  of  current  interest,  and  in  presenting 
the  subject  in  as  summary  a  manner  and  with 
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sound  method.  They  will  be  written  not  only 
for  the  specialist  but  for  the  educated  layman. 


PROTOPLASMIC  ACTION 
AND  NERVOUS  ACTION 


THE  UNIVERSITY  OF  CHICAGO  PBESS 
CHICAGO,  ILLINOIS 


THE  BAKER  AND  TAYLOR  COMPANY 

NEW   YORK 


THE  CAMBRIDGE  UNIVERSITY  PRESS 

LONDON 

THE  MARUZEN-KABUSHIKI-KAISHA 

TOKYO,  OSAKA,    KYOTO,    FUKUOKA,   SENDAI 

THE  MISSION  BOOK  COMPANl 

SHANSHAI 


PROTOPLASMIC  ACTION 
AND  NERVOUS  ACTION 


Ralph  S.  jLillie 

Biologist,  Nela  Research  Laboratories,  Cleveland;  formerly 
Professor  of  Biology,  Clark  University 


What  am  I,  Life  ?   a  thing  of  watery  salt, 
Held  in  cohesion  by  unresting  cells  .  .  .  .   ? 

— Masefield 


THE  UNIVERSITY  OF  CHICAGO  PRESS 
CHICAGO  ILLINOIS 


Copyright  1Q23  By 
The  University  of  Chicago 


All  Rights  Reserved 


Published  October  1023 


Composed  and  Printed  By 

The  University  of  Chicago  Press 

Chicagfo,  Illinois,  U.S.A. 


LIBRARY 

Nm  C-  State  Oo/Jege 


TO 

HELEN  MAKEPEACE  LILLIE 


i^j 


PREFACE 

The  present  volume  is  based  in  part  on  lectures 
delivered  in  Clark  University  and  the  Marine  Biological 
Laboratory,  on  the  physico-chemical  basis  of  the  more 
general  or  fundamental  properties  of  living  matter. 
Common  to  all  forms  of  living  matter  are  certain  proper- 
ties or  modes  of  action  which  are  absent  or  imperfectly 
developed  in  non-living  matter.  The  chief  of  these  are 
(i)  the  property  of  specific  growth,  and  (2)  a  unification 
or  integration  of  activities,  of  such  a  kind  as  to  secure  the 
continued  existence  of  the  Hving  system  in  its  environ- 
ment. The  question  of  how  the  living  system  must  be 
constituted  (in  the  physico-chemical  sense)  in  order  to 
exhibit  such  properties  is  the  fundamental  one  for 
physiology. 

Of  late  years  the  analytical  investigation  of  the 
living  organism  and  its  products  has  made  great  advances; 
on  the  synthetic  side,  however,  progress  has  been 
relatively  slight.  The  precise  manner  in  which  certain 
special  physico-chemical  materials  and  i)rocesses  arc 
combined  so  as  to  produce  life  still  remains  largely 
obscure.  It  may  be  expected  that  properly  directed 
experiment  will  throw  light  on  this  problem,  as  it  has 
on  many  others  apparently  equally  dilTicult.  but  at 
present  we  are  at  a  stage  where  exact  or  scientific  knowl- 
edge is  only  in  its  beginning. 

In  this  book  I  have  made  no  attempt  to  consider  in 
detail  the  many  special  problems  of  pure  ])hysics  and 
chemistry  which  are  presented  by  the  organism.     It  is 

ix 


X  PREFACE 

assumed  that  these  problems  are  of  the  same  kind,  and 
to  be  approached  by  the  same  methods,  as  other  problems 
of  physics  and  chemistry.  This  point  of  view  seems  the 
only  one  possible  for  the  scientific  investigator.  The 
organism  exhibits  a  regularity  which,  although  of  a 
special  kind,  is  obviously  based  upon  and  presupposes 
the  regularity  of  its  component  physico-chemical  proc- 
esses. Investigation  of  the  latter  requires  the  use  of 
the  exact  methods  developed  by  modern  analysis;  and 
these  have  been  shown  to  yield  the  same  constant  and 
reproducible  results  in  organisms  as  in  non-living 
systems.  In  fact,  one  of  the  most  striking  features  of 
organic  processes  is  their  exactitude,  which  is  frequently 
safeguarded  by  regulatory  devices  of  the  utmost  delicacy. 
The  investigation  of  many  such  processes  is  purely 
physico-chemical  in  its  method  and  results. 

It  must  be  remembered,  however,  that  in  living 
organisms  we  are  dealing  with  synthetic  products  of  a 
higher  order.  When  the  materials  and  energies  of  the 
surrounding  world  unite  to  constitute  the  organism, 
new  qualities  and  modes  of  activity  inevitably  come  into 
existence;  these  special  properties  of  living  beings  form 
the  subject-matter  of  the  biological  sciences,  as  dis- 
tinguished from  the  physical  sciences.  For  this  reason 
the  physical  and  chemical  characterization  of  the  con- 
stituents, reactions,  and  processes  whose  combination 
or  synthesis  produces  Hfe  is  not  in  itself  sufficient; 
the  biological  interest  centers  in  the  conditions  and 
special  mode  of  this  combination,  and  in  the  nature 
of  the  resulting  unity.  The  problem  of  the  nature 
of  vital  organization  remains  the  fundamental  one  for 
biology. 


PREFACE  Xi 

We  may  safely  assume  that  all  fjualilative  phenomena, 
including  those  of  the  living  organism,  are  subject  to 
quantitative  laws;  but  the  determination  of  these  laws, 
while  an  essential  object  of  scientific  investigation, 
cannot  be  regarded  as  its  only  object.  The  biologist  is 
primarily  interested  in  the  phenomena  which  are  peculiar 
to  life  and  in  the  conditions  under  which  these  originate 
and  manifest  themselves.  As  already  indicated,  growth, 
development,  and  an  integrative  correlation  of  activities 
are  the  chief  distinguishing  characters  of  organisms. 
Underlying  and  determining  these  properties  are  the 
fundamental  or  universal  properties  of  protoplasm. 
The  essential  problem  in  the  physiolog}^  of  growth  (and 
ultimately  of  development  and  heredity)  is  the  problem 
of  the  conditions  of  specific  chemical  synthesis  in  proto- 
plasm. And  the  problem  of  integration  resolves  itself 
largely  into  the  problem  of  the  conditions  under  which 
protoplasmic  processes,  although  spatially  separated, 
mutually  influence  one  another;  i.e.,  the  problem  of 
transmission.  For  the  solution  of  these  problems  we 
require  first  of  all  a  knowledge  of  the  special  conditions 
under  which  the  chemical  reactions  in  protoplasm 
proceed  and  influence  one  another. 

The  general  physical  conditions  under  which  chemical 
reactions  are  initiated,  accelerated  or  retarded,  and 
influence  other  reactions  at  a  distance  are  undoubtedly 
the  same  in  living  as  in  non-living  matter;  but  the  sjx^cial 
features  of  composition  and  arrangement  in  the  proto- 
plasmic system  often  render  detailed  analysis  difficult. 
Under  these  circumstances  the  study  of  "models" — 
simple  artificial  systems  in  which  the  action  of  single 
factors  may  be  isolated  and  observed  —may  be  of  great 


xii  PREFACE 

service,  and  I  have  made  use  of  this  method  in  a  number 
of  instances.  For  example,  the  transmission  of  the 
effects  of  stimulation  in  nerve  and  other  irritable  forms 
of  protoplasm  resembles  closely  certain  types  of  chemical 
transmission  or  distance-action  in  metal-electrolyte 
combinations;  many  biocatalytic  reactions  are  identical 
with  those  induced  by  colloidal  platinum  or  charcoal; 
there  are  also  instructive  analogies  between  organic 
growth  and  certain  types  of  inorganic  growth.  Many 
fundamental  physical  processes  which  play  an  important 
part  in  protoplasm  are  independent  of  the  special 
chemical  composition  of  the  material;  thus  the  influence 
of  radiation  and  electricity  on  living  matter  is  a  special 
case  of  the  general  influence  which  these  agents  exercise 
under  appropriate  conditions  upon  all  chemical  reactions. 
The  detailed  nature  of  the  conditions  in  protoplasm  can 
be  determined  only  by  special  investigation. 

The  more  special  sections  of  this  book  have  reference 
to  the  two  fundamental  problems  above  defined.  The 
structural  and  physico-chemical  organization  of  living 
matter,  the  modifiability  of  its  rate  of  reaction  under 
varying  conditions  (irritability),  and  its  transmissive 
property  (so  highly  developed  in  nervous  tissues)  are 
considered  in  some  detail;  and  their  probable  relation 
to  the  pol>^hasic  and  film-partitioned  character  of  the 
protoplasmic  system  is  indicated. 


CONTENTS 

CHAPTER  p^^.^ 

I.  Introduction— General  Ciuractkristics  of  Lin- 
ing Matter j 

II.  The  Cellular  Organization  of  Living  ^L\ttkr  .       14 

III.  General  Characters  of  Living  Organisms  25 

IV.  General  Peculiarities  of  Protoplasm  as  a  Piiysi« 

CAL  System 48 

V.  Physical  Nature  of  Protoplasaiic  Structure:  Imt 

PORTANCE  OF  SURFACE  CONT)ITIONS 66 

\1.  Protoplasmic    Structure    {Continued):     Perme.-v- 

BILITY    AND    OtHER    PROPERTIES    OF    PROTOPLASMIC 

Membranes 98 

\'IL  General  Contritions  Determining  the  Properties 

OF  Protoplasmic  Membranes 1,^2 

MIL  REL.A.T10N  OF  the  Inorganic  Salts  of  the  Mediu.m 

TO  the  Physiological  Processes  in  Protoplasm        151 

IX.  General  Physiological  Action  of  Lipoid-Altp:r- 

ant  and  Surface-Active  Substances      .  '  "^  7 

X.  Catalysis   in   Relation   to   the   Chemical   Pro- 
cesses in  Living  Matter j  1 7 

XL  Electrical  and  Other  Factors  in  the  Catalytic 

Action  of  Protoplasm -  ;5 

XII.  Stimulation  and  Transmission  of  Excitation  in* 

Protoplasm -^59 

XIII.  Bioelectric  Phenomena 200 

XIV.  Membrane  Changes  during  Stimulation  ;  ^7 

XV.  The  Physico-Chemical  Basis  of  Transmission  in 

Nerve  and  Other  Protoplasmic  Systems  s:\) 

Index 4" 

xiii 


I 


CHAPTER  I 

INTRODUCTION— GENERAL  CHARACTERISTICS 
OF  LIVING  MATTER 

It  is  a  peculiarity  of  living  matter,  as  distinguished 
from  non-living  matter,  that  it  is  never  found  in  a 
diffuse,  unorganized,  or  formless  state,  but  always 
composing  definite  individualized  systems  or  organisms, 
of  which  there  are  many  kinds  or  species,  each  with 
definite  and,  on  the  whole,  highly  constant  physico- 
chemical,  structural,  and  active  characters.  These 
organisms  form  a  class  of  natural  systems  which,  con- 
sidered quantitatively,  is  a  very  small  one  in  comparison 
with  physical  nature  as  a  whole.  This  fact  in  itself 
implies  that  living  systems  are  highly  special  develop- 
ments; they  represent  a  higher  order  of  synthesis,  and 
it  is  to  be  expected  that  they  should  exhibit  ])ro])crties 
and  activities  which  are  absent  in  non-living  systems. 
Hence  the  existence  of  a  sharp  contrast  between  the 
living  and  the  non-living — i.e.,  between  organism  and 
environment — is  not  in  itself  surj^rising.  We  know, 
however,  that  continuous  transitions  from  the  one  to 
the  other  have  existed  and  still  exist;  life  has  evolved 
from  non-living  matter  in  the  past;  and  in  the  present 
every  living  organism  is  the  seat  of  a  continual  trans- 
formation of  non-living  into  living  matter.  The  chief 
problem  of  general  physiologA'  is  to  trace  the  steps  of 
this  transition;  i.e.,  to  detemiine  the  nature  of  the 
synthesis  by  which   the   living  matter,   protoplasm,   is 


2  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

built  up  from  the  non-living  material  which  it  incorpo- 
rates from  the  surroundings. 

Physiology  regards  the  living  organism  solely  in  its 
objective  aspect  as  a  physical  object  in  external  nature; 
many  aspects  and  manifestations  of  living  beings  do  not 
form  directly  a  part  of  its  subject-matter,  and  the  general 
philosophical  question  of  the  essential  significance  of  life 
in  the  cosm^os — the  question  of  vitalism  or  anti- vitalism 
— is  not  one  which  it  makes  any  pretensions  to  answer. 
It  observes  simply  that  certain  systems,  living  organisms, 
exist  in  the  external  world,  presenting  a  remarkable 
combination  of  properties  not  found  in  other  natural 
systems;  and  its  task  is  the  analysis  of  these  systems  in 
the  terms  and  by  the  methods  of  physical  science. 

These  special  or  distinguishing  peculiarities  of  living 
organisms  may  be  grouped  under  several  general  heads, 
as  follows:  (i)  metabolism,  (2)  growth,  automatic  self- 
maintenance,  reproduction  and  heredity,  (3)  irritability, 
(4)  regulation  and  adaptation,  (5)  spontaneous  activity, 
having  reference  to  future  as  well  as  present  conditions. 
The  essential  character  and  implications  of  these  various 
properties  will  first  be  briefly  considered. 

I.      METABOLISM 

The  essential  peculiarity  which  places  organisms  in 
a  class  apart  from  most  non-living  objects  is  that  their 
properties  and  manifestations  depend  on  their  continued 
chemical  activity;  in  other  words,  they  are  metabolizing 
systems,  formed,  maintained,  and  perpetuated  by 
processes  of  chemical  transformation.  The  production 
of  new  chemical  compounds  by  transformation  of  other 
compounds    taken    from    the    surroundings,    and    the 


CHARACTERISTICS  OF  LIVING  .MATTER  3 

organization  of  these  compounds  in  new  structural  and 
chemical  relationships,  constitute  the  fundamental  activi- 
ties of  all  living  matter.  Hence  a  consideration  of 
the  general  features  of  metabolic  processes  must  come 
first  in  any  discussion  of  the  nature  of  protoplasmic 
action. 

Under  the  term  metabolism  are  included  primarily 
the  nutritive  and  energy-yielding  chemical  processes  in 
protoplasm,  and  secondarily  the  other  chemical  processes 
subserving  or  underlying  these.  The  application  of  the 
term  is  usually  clear;  but  metabolic  processes  comprise 
chemical  reactions  of  all  kinds,  many  of  which  are  in  no 
sense  peculiar  to  organisms,  while  others  are  not  met 
with  elsewhere  in  nature.  The  traditional  distinction 
between  constructive  and  destructive  metabolism  remains 
an  essential  one;  what  the  organism  is  at  any  time  is  a 
resultant  of  the  effects  of  these  two  large  and,  in  general, 
oppositely  directed  groups  of  chemical  reactions. 
Broadly  speaking,  the  constructive  reactions  represent 
the  nutritive  processes,  and  the  destructive  reactions 
the  energy-yielding  processes.  Constructive  metabolism 
includes  the  synthetic  (anabolic)  reactions  underlying 
growth,  self-maintenance,  and  reproduction.  In  any 
species  the  end-products  of  the  constructive  sequence  of 
reactions  consist  largely  of  certain  colloidal  compounds, 
highly  individualized  and  specific  in  their  chemical 
constitution,  the  proteins;  the  other  synthetic  products 
(carbohydrates,  fats,  lipoids,  etc.)  are  chemically  non- 
specific; i.e.,  not  confined  to  the  species  in  question; 
these  form,  together  with  the  specific  compounds,  water 
and  various  dissolved  substances,  a  complex  and  highly 
organized  system,  or  organic  individual,  wliich  is  specific 


4  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

(i.e.,  definitely  characterized  and  unique)  in  its  structural 
and  active  characters.  This  building-up,  by  means  of 
metabolic  construction,  of  a  complex  system,  specific  in 
chemical  composition,  structure,  and  activity,  out  of 
relatively  simple  non-specific  materials  taken  from  the 
surroundings  (food,  water,  salts)  is  the  fundamental 
general  peculiarity  which  distinguishes  living  organisms 
from  non-living  systems.  Constantly  associated  with 
the  constructive  group  of  reactions  is  the  destructive  or 
catabolic  group  by  which  substances  contained  in  the 
protoplasm  are  broken  down,  usually  oxidized,  to  yield 
the  energy  freed  in  vital  activity.  A  great  diversity  of 
compounds  are  thus  utilized  by  protoplasm  as  sources  of 
energy;  the  catabolic  process  is  non-specific;  i.e.,  sugars, 
fats,  and  proteins  are  metabolized  to  yield  the  same  end- 
products  (CO2,  water,  urea,  etc.)  and  energy  in  organisms 
of  all  kinds. 

2.      GROWTH,  MAINTENANCE,  REPRODUCTION, 

AND  HEREDITY 

It  is  essential  at  the  beginning  of  any  study  of 
fundamental  vital  properties  to  recognize  the  dependence 
of  the  various  phenomena  designated  by  the  four  terms 
above  upon  the  fundamental  process  of  specific  construc- 
tive metabolism.  In  every  organic  individual  normal 
self-maintenance,  by  which  the  material  lost  as  a  result 
of  metabolic  destruction  is  replaced  by  new  construction, 
involves  the  same  specific  synthetic  reactions  as  those 
concerned  in  growth.  And  growth  is  obviously  a 
highly  specific  process;  this  becomes  evident  whenever 
a  seed  or  an  egg  ''grows  into"  the  specifically  organized 
adult.     Organic  growth  thus  involves  or  implies  ''hered- 


CHARACTERISTICS  OF  LIVING  MATTER  5 

ity";  and  since  growth  is  the  foundational  life-process— 
that  by  which  all  living  matter  is  brought  into  existence 
— we  see  at  once  that  the  specificity  of  the  underlying 
metabolic  syntheses  is  the  essential  condition  underlying 
organic  specificity.  When  constructive  metabolism 
ceases,  not  only  does  growth  cease  but  life  itself,  since 
the  continual  formation  of  specific  material  is  a  i)rc- 
requisite  for  normal  maintenance. 

Each  of  the  terms  above,  however,  designates  a 
feature  or  aspect  of  vital  phenomena  which  is  as  a 
rule  perfectly  definite  and  distinguishable  from  the 
others.  Organic  growth  is  perhaps  best  defined  as 
increase  in  the  quantity  of  the  specifically  organized 
living  material.^  Reproduction  is  the  formation  of  new 
individuals  by  growth  from  the  parent  organism  or  a 
detached  portion  of  the  latter  (germ,  gamete);  in 
metazoa  the  replacement  of  outworn  or  senescent 
individuals  is  thus  accomplished.  Reproduction  has 
been  defined  as  "discontinuous  growth";  thus  the 
growth  of  a  plant-cutting  is  a  reproduction,  and  many 
cases  of  asexual  reproduction  in  animals  illustrate  the 
same  phenomenon  (reproduction  by  fission,  regeneration). 
In  the  lowest  organisms,  e.g.,  bacteria,  it  becomes  no 
longer  a  matter  of  practical  interest  to  distinguish 
between  growth  and  reproduction.  Heredity,  the  re- 
semblance of  offspring  or  outgrowth  to  parent  stock,  is 
illustrated  in  all  of  these  cases;  the  special  problem  of 
heredity,  therefore,  is  reducible  ultimately  to  the  funda- 
mental problem  of  the  conditions  determining  the 
property  of  specific  construction  possessed  by  all  forms 

'  Cf.  the  discussion  by  Child,  Senescence  and  Rcjuvcnrsrence,  Chic.ipo 
(191 5),  chap.  ii. 


6  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

of  protoplasm.^  This  consideration  is  overlooked  in 
many  ''theories  of  heredity,"  which  apparently  take  for 
granted  the  existence  of  the  property  which  they  are 
called  upon  to  explain.  Ids,  pangenes,  chromosomes, 
and  the  other  representative  particles  of  these  theories 
are  self-multiplying  units;  i.e.,  they  possess  ex  hypothesi 
this  automatic  power  of  synthesizing  material  and 
structure  of  their  own  kind.  It  is  well,  therefore,  to 
realize  clearly  the  fundamental  identity  of  the  physi- 
ological conditions  underlying  all  of  the  phenomena 
grouped  under  the  foregoing  head. 

To  prevent  any  possible  misunderstanding,  a  few 
words  may  be  added  here  concerning  the  nature  of  the 
physiological  problems  raised  by  the  chromosome 
theory  of  heredity,  which  now  seems  to  be  established 
on  a  secure  basis  through  the  correlation  of  genetic  and 
cytological  investigation.^ 

All  the  evidence  indicates  that  the  chromosomes, 
the  carriers  of  genetic  factors  or  "genes,"  are  the  elements 
or  units  in  a  sorting  and  distributing  mechanism,  by 
means  of  which  special  formative  metabolic  processes 
are  localized  in   definite   regions   of   the   growing   and 

^  Haldane's  remarks  in  his  British  Association  address  of  1908 
{Nature,  LXXVIII,  555),  "nutrition  itself  is  only  a  constant  process  of 
reproduction"  and  "heredity  is  for  biology  an  axiom  and  not  a  prob- 
lem," do  not  dispose  of  the  problem  of  heredity,  but  apparently  assign 
it  to  a  border-line  position,  somewhere  between  chemistry  and  biology. 
The  property  of  automatic  specific  synthesis  is  the  one  to  be  explained. 
The  original  natural  systems  which  exhibited  this  property  were  pre- 
sumably the  ones  from  which  living  organisms,  as  we  find  them,  have 
evolved. 

^  Cf .  T.  H.  Morgan,  The  Physical  Basis  of  Heredity,  Philadelphia 
(1919);  also  "The  Mechanism  of  Heredity,"  Nature,  CIX  (1922), 
241,  275,312. 


CHARACTERISTICS  OF  LIVING  MATTER  7 

developing  organism.  The  property  of  self-multiplica- 
tion possessed  by  these  units,  on  which  the  possibility 
of  their  special  action  depends,  is,  however,  not  peculiar 
to  them,  as  already  pointed  out,  but  is  a  property  of 
protoplasm  and  of  protoplasmic  structures  in  general.' 
Once  the  chromosomes  have  been  produced  by  this 
autosynthetic  process,  they  are  free  to  exercise  their 
special  influence  and  function.  In  this  respect  they 
are  like  other  structures  which  are  definite  factors  in 
the  formative  processes;  they  must  first  be  synthesized 
by  the  fundamental  growth  processes  before  they  can 
function.  There  are  obvious  analogies  between  the 
action  of  the  chromosomes  and  the  action  of  special 
form-determining  chemical  substances  (or  hormones) 
produced  by  various  organs.  Development  at  certain 
stages  is  demonstrably  a  consequence,  as  regards  certain 
special  features,  of  the  previous  development  of  the 
thyroid  or  the  pituitary  gland  or  the  gonads.  An  even 
more  general  analogy  may  be  pointed  out  here,  since 
it  illustrates  the  nature  of  many  biological  sequences. 
A  prerequisite  to  the  normal  activity  of  the  adult  is  the 
development  of  the  normal  adult  structure;  for  example, 
the  formation  of  hands  must  precede  the  construction  of 
a  house,  but  we  do  not  explain  the  whole  constructive 
process  by  reference  to  the  hands,  the  tools  for  sorting 
and  distributing  the  materials.  How  the  chromosomes 
influence  formative  metabolism  is  the  essential  problem 
for  physiolog}^;  this  problem  is  at  present  unsolved,  but 
there  can  be  no  doubt  as  to  the  existence  of  this 
influence. 

^  H.  J.  MuUer  has  discussed  the  properties  of  the  genes  from  this 
point  of  view  in  a  recent  paper  in  American  Naturalist^  LVI  (1922),  32. 


8  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

3.      IRRITABILITY 

It  is  characteristic  of  all  organisms  that  they  respond 
to  changes  in  their  environment  (stimuli)  by  changes  in 
their  own  activity  (response).  And  since  metabolic 
reactions  underlie  all  vital  activity,  this  fact  implies 
that  the  chemical  reactions  constituting  metabolism 
are  subject  to  the  influence  of  external  agencies  acting 
upon  the  protoplasm.  Both  constructive  and  destruc- 
tive metabolism  may  be  thus  influenced. 

In  general,  what  we  mean  by  irritability  is  this 
susceptibility  to  external  influence;  irritability,  however, 
cannot  be  considered  as  a  special  property  independent 
of  the  continual  automatic,  chemical,  and  other  activity 
of  the  living  system;  its  existence  merely  shows  that 
the  chemical  reactions  of  protoplasm  are  subject  to 
modification — e.g.,  acceleration  or  the  reverse — under  the 
influence  of  relatively  slight  changes  of  state,  caused  usually 
by  the  action  of  external  agencies  upon  the  protoplasm. 

A  peculiarity  of  most  intact  organisms  is  that  the 
changes  of  activity  thus  induced  are  normally  of  such 
a  character  as  to  favor  the  continued  existence  of  the 
individual  or  of  the  species  in  the  environment;  this 
general  fact  may  be  expressed  by  saying  that  the  normal 
responses  to  stimulation,  however  varied  in  detail,  have 
a  regulative  or  adaptive  character.  Adaptiveness,  how- 
ever, is  a  peculiarity  of  the  organism  as  a  whole,  not  an 
inherent  property  of  protoplasm  in  general;  this  is 
shown  by  the  fact  that  isolated  parts  may  show  irrita- 
bility quite  independently  of  any  adaptive  reference; 
e.g.,  nerve  or  muscle.  In  this  respect  irritability  may  be 
compared  with  the  chemical  instability  of  explosives, 
which  may  also  be  applied  adaptively. 


CHARACTERISTICS  OF  LIVING  MATTER  9 

4.      REGULATION  AND  ADAPTATION,  INTEGRATION 

These  characters,  while  based  on  irritalMlily,  have  a 
more  distinctively  organic  or  vital  quality — are  manifes- 
tations of  a  higher  plane  of  organization — than  the  simple 
property  of  responsiveness  to  stimuli.  Fundamentally 
they  are  related  to  the  characteristic  self-conserving 
property  of  the  organic  individual  or  species;  this  prop- 
erty is  exhibited  by  all  naturally  occurring  organisms, 
i.e.,  the  structure  and  activity  of  the  latter  are  of  such 
a  kind  as  to  favor  a  permanent  or  stable  existence  in  the 
environment.  Under  the  terms  regulation  and  adapta- 
tion, we  include,  in  their  broadest  application,  all  of 
those  features  of  adjustment — structural,  chemical,  and 
active — which  are  especially  characteristic  of  li\ing  as 
distinguished  from  non-living  systems.  The  organism 
is  ''fitted"  to  its  environment;  the  reciprocal  relations 
between  the  two  are  so  balanced  or  correlated  that  the 
species  persists.  In  other  words,  the  properties  or 
activities  which  have  special  ''survival  value"  are  those 
which  we  designate  as  adaptive.  Adaptations  may  be 
(i)  of  a  static  or  morphological  kind — non-temporal  in 
their  reference — e.g.,  when  the  structure  of  the  organism 
shows  a  correspondence  with  the  unchanging  features  of 
its  environment.  Perhaps  the  most  general  and  wide- 
spread example  of  such  static  adaptation  is  seen  in  the 
general  plan  of  bodily  structure  common  to  most  free- 
living  animals — bilateral  s^nmietry  combined  with 
antero-posterior  and  dorso-ventral  dilTerentiation.'     Or 

^  I  have  discussed  more  fully  the  general  conditions  that  render 
this  type  of  structural  plan  adaptive  in  a  paper  on  purposive  and  adap- 
tive behavior  in  the  Journal  of  Philosophy,  Psychology  and  Scientific 
Methods,  XII  (1915),  589. 


lo  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

they  may  be  of  an  active  kind;  such  are  classed  as 
regulations.  In  this  case  the  activity  of  the  organism 
or  of  its  parts  changes  in  such  a  way  as  to  resist  or 
compensate  departure  from  the  normal;  i.e.,  from  the 
physiological  or  other  conditions  required  for  continued 
life.  The  automatic  regulation  of  food-intake,  gaseous 
exchange  or  temperature,  the  protective  and  other 
self-conserving  reactions  or  instincts,  and  the  phenomena 
of  form-regulation  are  examples.  Since  in  all  such  cases 
the  persistence  of  the  organism  in  the  environment  is 
the  condition  promoted  or  secured,  and  since  persistence 
in  external  nature  implies  equilibrium,  we  may  character- 
ize regulations  as  reactions  of  an  equilibrating  type; 
i.e.,  regulation  corresponds  essentially  to  equilibration. 
In  a  sense  it  is  obvious  that  the  structure  and  activities 
of  an  organic  species  must  be  such  as  to  secure  persistence 
in  the  environment,  since  the  alternative  is  extinction; 
nevertheless  the  universal  presence  of  regulative  modes 
of  activity  is  a  peculiar  and  highly  remarkable  feature 
of  living  as  distinguished  from  non-living  systems,  and 
requires  special  consideration.  Regulations  or  automatic 
equilibrations  are  also  met  with  in  many  non-living 
systems  (regulators  in  machines  or  other  artificial 
systems),  but  for  the  most  part  these  are  of  a  relatively 
simple  type. 

The  conception  of  organic  integration  is  closely 
related  to  that  of  regulation;  the  maintenance  of  a 
definite  and  unified  structure  and  activity  in  any  complex 
system  consisting  of  many  parts  requires  the  mutual 
interaction  and  control  of  the  different  parts  in  such  a 
manner  that  the  activity  of  each  is  subordinated  to  that 
of  the  whole.     This  integration  presupposes  the  trans- 


CHARACTERISTICS  OF  LIVING  MATTER  1 1 

mission  of  chemical  and  other  influence  between  different 
regions,  and  in  higher  organisms  is  effected  chiefly 
through  the  nervous  system  in  co-operation  with  a  chemi- 
cal control  exercised  by  special  substances  (hormones 
and  other  metaboHc  products)  transported  from  place  to 
place  in  the  circulation.'  The  possibility  of  these  two 
forms  of  integration  rests  ultimately  on  mechanical  or 
structural  factors,  shown  in  the  permanence  of  morpho- 
logical form  and  organization;  hence  some  authors  speak 
of  a  mechanical  integration  (or  correlation)  in  addition 
to  the  other  two.^ 

5.      SPONTANEOUS  ACTIVITY 

The  chief  vital  phenomena  classed  under  this  head 
are  characteristic  of  the  organism  in  its  action  as  a 
whole,  rather  than  of  its  special  parts,  although  many  of 
these  are  spontaneously  active;  e.g.,  the  heart.  They 
are  especially  developed  in  animals,  and  include  spon- 
taneous activity  and  trains  of  activity  (instincts) 
directed  toward  the  external  world  and  having  usually 
some  definite  future  reference;  purposive  and  conscious 
action,  in  their  physiological  aspect,  also  belong  here. 
All  such  characters  are  based  upon,  or  presuppose, 
the  other  more  fundamental  characters;  i.e.,  they  are 
not  general  protoplasmic  properties  but  appear  at 
a  higher  level  of  vital  synthesis;  hence  they  do  not 
form,  strictly  speaking,  a  part  of  our  present  subject- 
matter. 

^  Cf.  Sherrington's  Integrative  Action  of  the  Nervous  System. 

^  Cf .  Child,  The  Origin  and  Development  of  the  Ncrvot4S  System  from 
a  Physiological  Viewpoint,  University  of  Chicago  Press  (1921),  chap,  i, 
p.  12. 


12     PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 
SCOPE  OF  GENERAL  PHYSIOLOGY 

The  first  four  groups  of  characters  appear  to  be 
common  to  all  forms  of  living  matter;  i.e.,  they  are  the 
expressions  of  the  general  or  fundamental  properties 
and  activities  of  the  living  substance  or  protoplasm 
wherever  found.  We  class  as  ''living"  all  natural 
systems  exhibiting  these  properties  in  combination;  and 
general  physiology  has  for  its  object  the  study  of  the 
essential  composition  and  activities  of  such  systems. 

From  this  point  of  view  the  distinction  between 
animals  and  plants  becomes  one  of  minor  importance. 
This  difference  is  essentially  one  of  method  of  nutrition; 
in  plants  the  processes  of  constructive  metabolism  start 
with  more  elementary  and  widely  diffused  materials 
than  in  animals.  A  brief  reference  to  the  main  points 
of  distinction  seems  relevant  here,  since  it  may  assist 
in  defining  the  essential  problem  under  consideration. 

It  is  evident  that  all  organisms  require  for  their 
normal  growth  and  activities  the  presence  of  energy- 
yielding  (chiefly  oxidizable)  materials  in  the  protoplasm, 
as  well  as  materials  for  building  up-  protoplasmic  struc- 
ture; the  chief  representatives  of  these  two  classes  of 
substances  are,  respectively,  the  carbohydrates  and  the 
amino-acids.  The  main  differences  between  plants  and 
animals  relate  to  the  methods  by  which  these  materials 
are  obtained  or  rendered  available.  In  green  plants 
they  are  synthesized  from  simpler  compounds  which  in 
their  unaltered  state  cannot  serve  as  sources  of  energy — 
CO2,  salts,  water.  In  animals  the  chief  "food"  materials 
are  already  complex  compounds  of  high  chemical 
potential  which  are  not  synthesized  in  the  organism 
but  are  prepared  outside  of  the  latter  (ultimately  by 


CHARACTERISTICS  OF  LIVING  J\L\TTER  13 

plants),  and  are  introduced  into  the  organism  from 
without  by  its  own  special  activities.  In  both  groups, 
however,  the  active  living  substance  or  protoplasm 
consists  chiefly  of  compounds  of  the  same  general 
chemical  type,  which  in  both  cases  undergo  similar 
transformations.  The  fundamental  physiological  pro- 
cesses of  .plant  and  animal  cells  are  thus  closely  similar. 
Hence,  in  general  physiology,  whose  aim  is  the  analysis 
of  the  vital  process,  wherever  occurring,  organisms  of 
both  groups  come  equally  under  consideration. 


CHAPTER  II 
THE  CELLULAR  ORGANIZATION  OF  LIVING  MATTER 

General  physiology  has  been  defined  by  Verworn^ 
as  ''cellular  physiology,"  in  accordance  with  the  general 
conception  of  the  cell  theory  that  the  ultimate  living 
units  of  any  organism  are  the  cells.  According  to  this 
conception  the  cells  are  the  simplest  units  capable  of 
independent  life;  hence  general  physiology,  aiming 
at  the  analysis  and  characterization  of  life-processes, 
should  be  equivalent  to  cell  physiology.  There  appears, 
however,  to  be  a  certain  arbitrariness  in  this  idea. 
The  cell  is  already  a  complex  system  with  a  definite 
organization,  usually  containing  a  nucleus  and  exhibiting 
other  special  structural  differentiations.  The  question 
of  the  physiological  significance  of  the  cellular  organiza- 
tion constitutes  a  special  problem  in  itself.  While  it 
is  remarkable  that  all  higher  organisms  show  this  type 
of  organization,  it  seems  hardly  justifiable  to  regard  all 
organisms  as  consisting  of  cells  and  products  of  cells. 
Such  a  conception  regards  the  simplest  living  unit  as 
having  a  certain  definite  type  of  structural  organization; 
i.e.,  it  is  essentially  a  morphological  conception.  A 
chemical  characterization  seems  to  meet  the  requirements 
of  the  case  more  completely.  Many  organisms  are 
known  which  do  not  show  the  chief  structural  feature  of 
the  cell,  differentiation  into  nucleus  and  cytoplasm;  e.g., 
bacteria  and  blue-green  algae.  Usually  bacteria  are 
regarded  as  plant  cells  of  a  special  kind;   it  is  question- 

^  AUgemeine  Physiologie,  5th  edition,  Jena  (1909),  chap.  i. 

14 


CELLULAR  ORGANIZATION  OF  LIVING  .AIATTKR     15 

able,  however,  if  micrococci,  and  especially  the  organisms 
in  filterable  viruses,  can  be  considered  as  cells  in  the 
true  sense.  The  case  of  the  ultra-microscopic  organisms 
present  in  the  filterable  viruses  is  of  special  interest. 
These  organisms  can  be  demonstrated  only  by  the  effects 
which  they  produce  (infection);  they  prove  themselves 
to  be  living  by  their  power  of  automatic  growth,  shown 
by  multiphcation  in  the  body  of  the  host  or  in  culture- 
media,  and  also  by  exhibiting  other  properties  character- 
istic of  protoplasm  in  general,  such  as  thermolabihty 
and  susceptibility  to  toxic  agents  of  the  disinfectant 
class.  They  may  be  described  as  complex  and  chemically 
active  (metabolizing)  material  in  a  fine  state  of  sub- 
division (like  that  of  colloidal  material),  possessing  in 
addition  to  the  other  properties  of  matter  in  this  state 
the  special  vital  properties  of  assimilation,  growth,  and 
multiplication.  As  already  pointed  out,  this  ability  to 
transform  environmental  material  into  its  own  specifically 
organized  and  active  substance  is  the  distinctive  criterion 
of  living  as  distinguished  from  non-living  matter. 

Our  conceptions  of  the  nature  of  living  organisms 
must  be  broad  enough  to  include  the  ultra-microscopic 
forms.  Cells,  as  found  in  higher  organisms,  are  units 
of  a  relatively  complex  and  highly  differentiated  kind, 
representing  a  comparatively  advanced  stage  of  evolu- 
tion. They  are  by  no  means  to  be  regarded  as  the  only 
systems  in  nature  exhibiting  the  characteristics  of  life. 

THE  CELL 

In  higher  organisms,  however,  we  have  definite 
experimental  evidence  that  the  smallest  unit  ca]xible  of 
continued  independent  hfe  is  the  nucleated  cell,     i'he 


1 6  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

protozoa  remain  as  single  cells  throughout  life.  The 
higher  animals  and  plants  are  single  cells  only  at  the 
beginning  of  their  development — in  the  germ-cell  stage; 
in  later  developmental  stages  and  as  adults  they  consist 
of  large,  closely  associated  aggregates  or  colonies  of 
cells,  which,  together  with  the  intercellular  fluid  media 
serving  for  transport  (blood)  and  various  other  products 
of  cellular  activity  (skeletal  and  other  structures),  form 
a  complex  and  highly  integrated  system,  or  organic 
individual.  Each  cell  in  this  organism  is  to  be  regarded 
as  hving  and  capable  of  independent  existence  under 
appropriate  conditions. 

The  statement  that  single  isolated  cells  are  capable  of 
independent  life  has  been  shown  experimentally  to  be 
true,  not  merely  of  organisms  which  throughout  their 
life  are  unicellular,  but  also  of  many  of  the  cells  of  higher 
organisms  when  isolated  under  favorable  conditions — 
leucocytes,  ciliated  cells,  muscle  cells,  tissue-cells. 
Epithelial  cells  will  grow  in  suitable  culture-media;^ 
embryonic  nerve  cells,  isolated  in  sterile  plasma,  send 
out  axones  in  a  characteristic  manner;  i.e.,  retain  the 
normal  power  of  growth,  differentiation,  and  develop- 
ment;^ and  many  functional  adult  cells  continue  to 
live  and  grow  when  isolated  under  favorable  conditions 
of  food  and  oxygen  supply.^ 

On  the  other  hand,  experiment  shows  that  for  normal 
and    long-continued   vital   activity    the    cell   must    be 

^  Cf.  L.  Loeb,  Arch.  Entwickl.  Organ.,  XIII  (1:902),  487,  and  earlier 
papers  there  cited. 

'Harrison,  Proc.  Soc.  Exp.  Biol,  and  Med.,  Ill  (1907),  140;  Journal 
of  Experimental  Zoology,  IX  (1910),  797;  XVII  (1914),  521. 

3  Cf.  Carrel  and  Burrows,  Journal  of  Experimental  Medicine,  XIII 
(191 1);  W.  H.  and  M.  R.  Lewis,  Anatomical  Record,  VI  (191 2). 


CELLULAR  ORGANIZATION  OF  LI\'L\G  .^L^'rTKR     17 

complete,  at  least  in  the  sense  that  both  nucleus  and 
cytoplasm  (or  portions  of  both)  are  present.  This  is 
shown  by  experiments  on  enucleated  cells,  such  as  egg 
cells;  portions  containing  nuclei  survive;  the  others 
die.  But  if  enucleated  portions  are  fertilized  and  thus 
furnished  with  nuclei,  they  continue  to  live.'  An  other- 
wise complete  protozoon  such  as  Stcntor  will  die  if 
deprived  of  its  nucleus,  while  fragments  of  less  than 
one- twentieth  the  normal  size  will  survive  and  reform 
a  complete  organism  if  a  portion  of  nucleus  is  present. "^ 
Similar  results  have  been  obtained  in  experiments  on 
other  protozoa;  e.g.,  Verworn's  with  ThalassicoUa.^ 

There  is  a  large  body  of  similar  experimental  fact 
indicating  that  the  continued  interaction  of  nuclear  and 
cytoplasmic  components  is  an  essential  feature  of  nonnal 
cell-metabolism.  It  is  usually  supposed  that  the  nucleus 
has  special  relations  to  synthetic  metaboUsm;  hence 
its  special  importance  in  growth  and  regeneration,  but 
the  whole  problem  of  the  relation  of  nucleus  to  cytoplasm 
is  at  present  in  an  unsatisfactory  state."* 

It  is  clear,  nevertheless,  that  the  nucleated  cell  of  the 
higher  organism  is  a  complete  and  autonomous  living 
unit.  But  in  view  of  what  has  just  been  pointed  out 
regarding  the  non-cellular  or  subcellular  constitution  of 
some  organisms,  we  must  avoid  regarding  the  dis- 
tinctively cellular  features  of  protoplasmic  organization 

»  Cf.  Delage,  Arch,  de  zool.  cxp.  el  ghi.,  VII  (1899),  383. 

=«  F.  R.  Lillie,  Journal  of  Morphology,  XII  (1896),  239. 

aVerworn,  Arch.  ges.  Physiol.,  LI  (1891);  cf.  also  Allgcmcme 
Physiologic,  5th  edition  (1909),  p.  620. 

4  For  a  recent  study  cf.  V.  Lynch,  American  Journal  of  Physiology, 
XLVIII  (1919),  258. 


1 8  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

as  the  all-essential  ones.  To  do  so  would  be  to  imply 
that  in  the  early  or  precellular  stages  of  organic  evolution 
the  assimilative  or  proliferative  types  of  colloidal 
material,  which  presumably  were  then  the  only  systems 
representing  organisms,  were  not  living.  The  formation 
of  a  particular  kind  of  structure  is  not  the  essential 
criterion  of  vitality;  the  properties  which  underlie  the 
formative  or  structure-building  activities  are  the  primary 
ones.  In  most  animals  and  plants  these  activities  give 
rise  to  a  cellular  type  of  structure,  but  this  is  not  neces- 
sarily true  of  all. 

IMPORTANCE  OF  CELLULAR  ORGANIZATION 

There  is  a  sense,  therefore,  in  which  we  may  regard 
the  cellular  type  of  structural  organization  as  not  so 
much  the  cause  or  necessary  condition  of  the  vital 
activities  as  their  product  or  effect.  Obviously  all 
cellular  organisms  come  into  existence  through  the 
constructive  processes  of  growth.  This  was  pointed  out 
by  Huxley,  in  the  early  years  of  the  cell  theory,  in  a 
well-known  passage  in  which  he  speaks  of  the  cells  as 
being  not  the  producers  but  simply  the  products  or 
indicators  of  vital  action.  Like  the  shells  on  the. sea 
beach  the  cells  "mark  only  where  the  vital  tides  have 
been  and  how  they  have  acted."'  This  comparison  is 
an  apt  one  in  that  it  emphasizes  the  primary  importance 
of  the  structure-forming  vital  activity  which  expresses 
itself  in  the  formation  of  cells;  but  it  tends  perhaps  to 
subordinate  the  part  played  by  the  cellular  structure, 
once  it  has  been  attained.     There  is  no  doubt  that  this 

^  Cf.  Huxley,  "Review  of  the  Cell  Theory"  in  the  British  and  Foreign 
Medico-chiriirgical  Review  (1853), 


CELLULAR  ORGANIZATION  OF  LIVLVG  M A'lTFR     tq 

structure  detennines,  in  a  quite  special  way,  the  character 
of  the  protoplasmic  processes;  i.e.,  has  its  own  (Icfmitc 
causative  and  controlling  influence.  The  metabolic  and 
other  cell  processes  can  be  shown  to  be  profoundly 
influenced  by  changes  in  the  physical  and  other  state 
of  cell  structures.  For  example,  there  is  evidence  that 
in  most  cells  irritability  depends  primarily  upon  the 
special  properties  of  the  external  ])rotoplasmic  layer 
or  plasma  membrane;  the  contractile,  secretor}-,  and 
similar  mechanisms  are  cell  structures;  the  s])ecial 
relation  of  the  nucleus  to  constructive  metabolism 
has  already  been  mentioned.  In  general  we  may  say 
that  physiological  activity  in  all  higher  organisms  is 
intimately  bound  up  with  the  special  features  of 
structure,  chemical  organization,  and  activity  peculiar 
to  cells. 

A  universal  peculiarity  of  living  matter,  considered 
simply  as  a  chemical  reaction-system,  is  that  its  principal 
chemical  reactions,  especially  the  specific  constructive 
group,  occur  under  the  control  of  structural  conditions. 
If  protoplasmic  structure  is  destroyed,  mechanically  ur 
otherwise,  these  essential  vital  reactions  at  once  cease. 
New  structure  as  it  arises  in  growth  or  develojmient 
must  therefore  have  a  modifying  influence  on  the  meta- 
boUc  processes  and  the  other  physiological  processes 
dependent  upon  these.  The  structural  characters  pecu- 
liar to  cells  cannot  fail  to  influence  profoundly  the 
chemical  activity  of  all  living  systems  having  the  cellular 
type  of  organization.  One  of  the  fundamental  problems 
of  general  physiolog}:  has  reference  to  the  special  nature 
of  the  relations  existing  between  cellular  structure  and 
the  chemical  processes  of  the  cell  protoplasm. 


20  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

The  question,  Why  is  Hving  matter  so  characteristi- 
cally cellular  in  structure,  seems  to  be  equivalent  to  the 
question,  Why  is  it  partitioned,  subdivided  into  minute, 
usually  microscopical,  portions  (cells),  or  structurally 
discontinuous  ?  Each  portion  of  protoplasm  is  separated 
from  its  surrounding  medium  or  from  adjoining  cells 
by  a  thin,  structurally  distinct  boundary  layer  usually 
called  the  ''plasma  membrane";  and  the  presumption  is 
that  some  definite  physiological  advantage  attaches  to 
this  peculiarity.  The  most  evident  general  answer  is 
that  this  layer  serves  to  separate  or  insulate  the  living 
protoplasm  from  the  surroundings,  and  thus  to  protect 
it  from  the  disintegrative  or  otherwise  adverse  influence 
of  the  latter.  This  view  regards  the  plasma  membrane 
as  prunarily  a  protective  structure.  Through  its 
presence  each  separate  portion  of  living  substance,  or 
cell,  is  enabled  to  retain  its  special  composition  and 
individuality.  But  this  answer,  while  undoubtedly 
correct  in  part,  is  too  vague  and  general  to  be  satisfactory. 
The  recent  experimental  studies  on  protoplasmic  per- 
meabihty  have  thrown  a  more  definite  light  on  the 
problem.  They  have  shown  that  in  typical  living  cells 
the  external  protoplasmic  layer  has  the  properties  of  a 
semi-permeable  membrane;  i.e.,  it  is  impermeable  or 
difficultly  permeable  to  the  water-soluble  substances  of 
low  molecular  weight  present  in  the  protoplasm  and 
surroundings  (and  to  chemically  similar  substances), 
while  freely  permeable  to  water.  Free  diffusion  of 
soluble  substances  either  into  or  out  of  the  cell  is  thus 
prevented;  the  protoplasm  can  preserve  a  chemical 
composition  different  from  that  of  the  surrounding 
medium   without    the   interference    that   would    result 


CELLULAR  ORGAXIZA  TlOX  OF  LULXG  MA'ITKR     .i 

from  unrestricted  dilYusive  iiUerchan^f.'  Ii  i.^  t-\uiLiiL 
that  if  a  minute  portion  of  pr()t()i)lasm  is  to  retain  its 
special  chemical  organization,  il  must  he  protected 
against  loss  of  its  water-soluhle  constituents  hy  dilYusion, 
and  also  against  the  unregulated  entrance  of  soluble 
substances  from  without.  Chemical  analysis  shows 
in  fact  that  the  crystalloidal  content  of  living  cells  is 
ty})ically  widely  different  from  that  of  the  surrounchng 
medium.''  The  presence  of  a  (HlYusion-proof  partition 
separating  each  small  portion  of  living  j^rotoi^lasm  from 
its  surroundings  is  apparently  an  essential  feature  of  the 
cellular  organization. 

Without  such  a  diffusion-hindering  type  of  structure, 
it  is  difficult  to  see  how  a  high  degree  of  chemical  differ- 
entiation could  be  maintained  in  such  a  system  as  the 
living  organism,  consisting,  as  it  does,  in  large  part  of 
an  aqueous  solution  of  diffusible  substances.  Ditlerences 
in  the  distribution  of  soluble  substances  between  i)roto- 
plasm  and  surroundings  would  tend  to  ecjualize  them- 
selves by  diffusion,  and  chemical  differentiation  would 
become  difficult  or  impossible.  Alor])hological  dilTer- 
entiation  has  long  been  recognized  as  favored  by  the 
subdivision  of  the  developing  germ  into  cells;  this 
condition  permits  moq^hogenetic  i)rocesses  in  neighboring 
cells  and  cell  groups  to  proceed  in  relative  indei)en(lence 
of    one    another.^     In    a    similar    manner    an    essential 

*  Cf.  my  paper  in  Biological  Bulletin,  XVII  (iQog),  iSS,  for  a  fuller 
discussion. 

*  For  a  summary  of  work  in  this  field,  cf.  liulx-rs  I'  "-c 
Chemie  dcr  Zelle  und  dcr  Gcwcbe  (1914),  pp.  370.  4U>;  tf.  also  iioiu-^is 
article  in  Winlersteins  Handhuch  dcr  vcrgl.  Physiol.,  I  (191 1),  37. 

3  Cf.  F.  R.  Lillic,  "Adaptation  in  ClcavaKc,"  Woods  Hole  Btoi< 
Lectures  (1899),  p.  43. 


2  2  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

condition  for  the  isolation  of  chemical  and  physiological 
processes  in  adjacent  regions  of  the  organism  is  the 
presence  of  the  semi-permeable  intercellular  partitions. 

There  is  also  evidence  that  the  internal  protoplasm  of 
the  single  cell  is  frequently  pervaded  by  a  system  of  films 
or  closed  partitions  giving  a  chambered  type  of  structure ; 
and  the  possibility  of  intracellular  chemical  differentia- 
tion (''chemical  organization")  has  been  referred  to 
this  condition.^  Such  a  chambered  structure  corresponds 
essentially  to  that  of  an  emulsion-like  or  alveolar  system. 
Apparently  any  physico-chemical  system  which  is 
built  up  largely  of  water  and  substances  in  aqueous 
solution  must  be  a  partitioned  system  if  it  is  to  maintain 
within  a  small  space  a  high  degree  of  chemical  differ- 
entiation together  with  a  corresponding  diversity  of 
chemical  activity. 

In  general,  each  living  cell  can  be  shown  to  possess 
a  surface  layer  (plasma  membrane)  with  properties  differ- 
ent from  those  of  the  internal  protoplasm.  At  the  boun- 
dary between  this  surface  layer  and  the  adjoining  medium 
the  general  phenomena  characteristic  of  phase-boundaries 
are  exhibited.  A  highly  characteristic  feature  of  the 
living  cell  is  that  its  surface  is  sharply  defined  against 
the  medium,  like  the  surface  of  an  oil  drop,  very  much 
as  if  the  surface  layer  consisted  of  water-insoluble 
material.  This  water-immiscible  property  of  living 
protoplasm  and  the  semi-permeability  of  its  boundary 
layer  are  closely  associated  properties;  together  they 
constitute  one  of  the  most  notew^orthy  physical  peculiari- 
ties of  living  protoplasm.     Especially  significant  is  the 

*  Hofmeister,  Die  chemische  Organisation  der  Zelle,  Braunschweig 
(1901). 


CELLULAR  ORGANIZATION  OF  LRqNO  AT  N'l^ri- R     -n 

fact  that  they  arc  presencd  unly  while  the  cell  remains 
living.  All  cells  disintegrate  on  death;  the  vital  semi- 
permeability  and  water-immiscil)ility  are  then  lost. 
Any  living  cell,  such  as  a  blood  cor])uscle,  sus])en(ied 
in  its  normal  medium,  exhibits  general  i)hysical  ])n)perties 
similar  to  those  of  a  suspended  insoluble  particle;  e.g.,  an 
oil  drop.  These  properties  are  largely  an  expression  of 
general  physical  conditions  present  at  all  boundary 
surfaces  between  adjacent  phases,  and  their  consideration 
becomes  of  great  importance  to  the  physiologist. 

In  common  with  other  boundary-  surfaces  between 
mutually  immiscible  phases  the  cell  surfaces  have 
characteristic  electrical  properties  (interfacial  potential 
differences),  exhibit  surface  tension,  and  possess  the 
property  of  condensing  or  absorbing  dissolved  substances 
from  the  surrounding  solution  (adsorption).  The  general 
role  of  adsorption  in  protoplasmic  activity  is  a  highly 
important  one,  to  be  considered  later  in  more  detail; 
and  undoubtedly  this  process  is  a  chief  factor  in  the 
catalytic  or  quasi-catalytic  action  of  living  matter. 
In  general,  the  catalytic  properties  of  linely  divided 
substances,  such  as  charcoal  and  colloidal  metals,  arc 
referable — at  least  in  large  part— to  adsorption,  and  the 
same  is  probably  true  of  the  catalytic  properties  of  living 
cells.  Adsorption  appears  also  to  be  a  factor  in  the 
collection  of  nutrient  and  other  substances  from  very 
dilute  solution,  also  a  highly  characteristic  feature  of 
protoplasmic  activity. 

These  considerations  show  that  in  adtlition  to  limiting 
diffusion  and  thus  providing  for  structural  and  chemical 
differentiation  in  the  manner  indicated,  the  cellular  or 
partitioned  structure  of  li\ing  matter  is  physiologically 


24    P^TM'LASMIC  ACTION  AND  NERVOUS  ACTION 

imyorMfft  because  it  furnishes  the  conditions  for  another 
4^h^  characteristic  group  of  properties,  those  dependent 
^fej^isferface  conditions.  The  protoplasm  is  thus  enabled 
^P  rta  utilize  (so  to  speak)  the  special  physical  properties 
^.exhibited  by  matter  at  boundary  surfaces.  With  fine 
subdivision  the  proportion  of  surface  protoplasm  to  the 
total  mass  of  living  substance  is  large,  and  the  role  of 
surface  processes  assumes  corresponding  importance. 
This  general  point  of  view  recalls  Herbert  Spencer's 
explanation  of  cell-division  as  essentially  a  regulative 
process,  the  effect  of  which  is  to  maintain  a  certain 
minimal  surface-volume  ratio  in  the  protoplasmic  mass. 
The  living  substance  enters  into  relation  with  its  sur- 
roundings through  the  intermediary  of  a  surface  layer, 
which  has  special  physiological  properties,  in  corre- 
spondence with  the  special  nature  of  the  physical  condi- 
tions resident  at  boundary  surfaces.  Evidence  will  be 
presented  later  indicating  that  these  electrical,  adsorp- 
tive,  and  catalytic  properties  of  the  protoplasmic 
surface  layers  determine  many  of  the  most  characteristic 
features  of  protoplasmic  activity,  especially  the  automatic 
and  rhythmical  processes,  the  susceptibility  to  electrical 
influence,  and  the  v^arious  manifestations  of  irritability. 


CHAPTER  III 

GENERAL  CHARACTERS  OF  Ll\  IXG  ORGANISMS 

CHARACTERS  OF  ORGANISMS  IN  RELATION 
TO  ENVIRONMENT 

All  organisms  have  the  power  of  self-maintenance; 
i.e.,  of  maintaining  their  identity  and  a  certain  constancy 
of  structure,  chemical!  composition,  and  activity  in 
spite  of  continual  changes  in  their  surroundings  and  in 
their  own  living  substance.  The  degree  of  environmental 
change  to  which  different  organisms  are  exposed  varies 
greatly,  and  many  cells  of  higher  animals  pass  their 
whole  life  in  media  which  are  automatically  secured 
against  all  but  slight  variation.  On  the  other  hand, 
protoplasmic  activity,  implying  chemical  change,  is 
uninterrupted  during  Hfe;  and,  as  already  pointed  out, 
is  largely  the  expression  of  chemical  reactions,  chiefly 
oxidative  in  nature,  by  which  energy  is  freed.  In  all 
organisms  part  of  the  energy  thus  freed  takes  such  a 
form  that  the  organism  is  enabled  to  maintain  itself  in 
equilibrium  with  its  surroundings,  grow,  and  eN'entually 
reproduce  itself.  A  curious  and  highly  characteristic 
cycle  of  activity  is  thus  shown;  thus  the  animal  uses 
its  muscular  energy,  derived  from  the  oxidation  of 
carbohydrate,  to  secure  more  carljohydrate  and  other 
materials  which  serve  as  sources  of  vital  energy;  and 
this  cycle,  regulated  in  accordance  with  the  var>-ing 
physiological  requirements,  is  repeated  continually 
throughout  life.  Such  facts  illustrate  the  general  depend- 
ence of  life  upon  the  interchange  of  material  and  energy 

^5 


26    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

with  the  environment  and  explain  why  so  large  a  part 
of  biological  investigation  has  reference  to  the  inter- 
relations between  organism  and  environment. 

We  may  here  recall  Spencer's  characterization  of  life 
as  essentially  a  continual  adjustment  of  internal  to 
external  relations.^  Such  an  abstract  definition,  how- 
ever, appHes  to  many  other  systems  found  in  nature;  e.g., 
to  any  system  in  '' dynamic  equilibrium,"  such  as  a 
candle  flame,  a  whirlpool,  or  other  physical  system  in 
which  there  is  an  automatically  regulated  balance 
between  the  material  and  energy  supplied  to  the  system 
and  that  lost  to  the  environment.  Nevertheless,  it  is 
peculiarly  true  of  organisms  that  their  processes  are  of 
such  a  kind  as  to  maintain  constantly  a  certain  special 
complex  of  structural  and  active  characters  in  spite  of 
internal  and  external  changes.  The  requirements  for 
such  maintenance  vary  in  the  different  cases,  but  certain 
conditions  are  universal.  The  primary  condition  is 
that  material  must  be  taken  from  the  outside  that  will 
serve  (i)  as  a  source  of  energy  (to  replace  substances 
consumed  in  supplying  this  energy)  and  (2)  as  building 
material  for  the  structural  substratum  (protoplasm)  in 
which  the  energy-yielding  transformations  occur;  in 
this  second  class  are  included  substances  which  do  not 
serve  directly  as  sources  of  energy — e.g.,  inorganic  salts. 
Considered  from  the  most  general  point  of  view,  there- 
fore, the  living  organism  exhibits  (i)  a  continual  trans- 
formation of  material  taken  frona  its  surroundings  into  its 
own  specifically  organized  substance;  and  (2)  a  continual 
chemical  decomposition  of  portions  of  this  substance 
of  such  a  kind  as  to  furnish  free  energy  which  is  utilized 

^  Principles  of  Biology. 


GENERAL  CHARACTERS  OF  LIVING  ORGANISMS     27 

by  the  organism  in  the  characteristic  activities  (food- 
seeking,  etc.)  required  for  its  individual  maintcnanrc 
and  the  perpetuation  of  its  kind. 

From  this  general  point  of  view  the  simplest  cases 
are  the  most  instructive;  e.g.,  that  of  a  single  yeast 
cell  or  bacterium  introduced  into  a  nutrient  medium. 
The  organism  grows  and  divides  until  eventually  in 
place  of  the  single  cell  there  are  thousands.  Evidently 
the  material  of  these  additional  cells  comes  from  the 
surrounding  medium,  certain  constituents  of  which  arc 
transformed  into  the  living  material  or  protoi)lasm. 
The  total  quantity  of  material  in  the  whole  system, 
organism  plus  culture-medium,  is  unaltered;  but  its 
condition  has  undergone  a  profound  change.  A  typical 
nutrient  solution  for  yeast  (Pasteur's  solution)  contains 
sugar  and  various  salts  (NaK  tartrate,  chlorides,  phos- 
phates, and  sulphates  of  Na  and  K)  together  with  water 
and  oxygen.  From  these  relatively  simple  materials  are 
built  up  proteins,  lipoids,  fats,  and  other  complex  bodies; 
not  only  are  these  characteristic  substances  synthesized 
but  they  are  distributed  or  arranged  (partly  in  solid 
form)  in  a  definite  and  constant  manner  so  as  to  give 
rise  to  numerous  complex  and  uniformly  constituted 
systems,  the  yeast  cells.  Each  of  these,  once  formed, 
becomes  the  seat  of  further  transformations  of  the  same 
kind;  and  by  a  repetition  of  this  process  the  non-living 
material  of  the  medium  is  progressively  transformed 
into  living  protoplasm.  The  transformation  is  constant 
and  specific,  chemically,  structurally,  and  ])hysiologically ; 
''heredity"  receives  here  its  simplest  manifestation.* 

*  Cf.  my  paper,  "Heredity  from  a  Physico-Clicinical  Point  of  \i<\v, 
Biological  Bulletin,  XXXIV  (191 8),  65. 


28  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

All  organisms  and  all  cells  without  exception  possess 
this  power,  that  of  transforming  certain  materials 
selectively  appropriated  from  the  surroundings  into 
their  own  specifically  organized  and  chemically  active 
living  substance.  The  materials  used  by  different 
organisms  vary  widely  in  chemical  character  and  accessi- 
bility— contrast  the  case  of  a  yeast  cell  growing  in  a 
culture-medium  with  man  in  his  complex  social  environ- 
ment— but  in  every  case  the  essential  process  is  the 
transformation  of  non-living  environmental  material 
into  living  substance  of  a  constant  and  characteristic 
organization  and  activity. 

The  general  as  well  as  the  special  features  of  the 
organization  of  any  living  being  are  an  index  of  the  nature 
and  accessibility  of  the  environmental  materials  required 
for  its  maintenance.  This  is  well  illustrated  by  the 
general  morphological  and  physiological  contrast  between 
animals  and  plants.  Since  in  plants  constructive 
metabolism  begins  with  simple  mobile  or  diffusible 
materials  (CO2,  water,  salts),  present  everywhere  in  the 
soil  and  atmosphere,  there  is  no  need  for  locomotion; 
and  these  organisms  lead  typically  a  stationary  existence, 
remaining  rooted  to  one  spot  where  the  necessary 
materials  can  reach  them  by  diffusion.  The  typical 
radiating,  branching,  or  dichotomous  habit  of  growth, 
reaching  out  into  all  directions  of  space  and  thus  provid- 
ing a  large  area  of  surface  for  interchange,  is  an  '^  adapta- 
tion" to  this  general  environmental  condition.  Sessile 
animals  also  tend  to  acquire  a  radiating  plan  of  structure, 
as  illustrated  in  coelenterates  and  echinoderms.  In  the 
great  majority  of  animals,  however,  the  food  supplies 
have  to  be  selected  from  an  environment  containing 


GENERAL  CHARACTERS  OF  LIVING  ORGANLS.MS     29 

relatively  little  utilizable  and  much  non-utilizaljlc 
material.  In  such  a  case  self-maintenance  demands,  in 
addition  to  the  ability  to  move  from  place  to  place,  a 
selective  power  of  reaction  by  which  food  materials 
may  be  picked  out  and  incorporated.  AccordinL^dv  the 
responsiveness  to  external  changes  (irritability,  motor 
activity)  reaches  its  highest  development  in  this  group 
of  organisms.  The  development  of  locomotor  powers 
is  especially  characteristic  of  animals;  related  to  this 
is  their  great  variety  of  reactions  and  instincts.  From 
such  general  considerations  we  may  see  in  a  general  way 
how  the  distinguishing  or  prevailing  characters  of  each 
group  have  arisen  in  evolution  in  correspondence  with 
the  differences  in  their  methods  of  nutrition. 

In  all  organisms  this  selection  of  assimilable  material 
from  the  environment  and  its  transformation  into  living 
protoplasm  proceed  automatically  and  are  regulated  in 
correspondence  with  the  physiological  requirements,  as 
these  vary  w^ith  the  changes  of  activity  and  of  external 
conditions.  Both  the  automaticity  and  the  regulated 
character  of  these  activities  are  well  illustrated  by  the 
changes  in  the  reaction  of  animals  to  food  materials 
during  periods  of  ''hunger."  Consumption  of  the 
energy-yielding  reserves  within  the  living  protoplasm 
leads  to  an  increased  reactivity  of  the  whole  organism 
to  these  substances.  Through  this  means  the  mainte- 
nance of  the  metabolic  equilibrium  is  assured  under  the 
usual  conditions.  Regulation  of  this  kind  is  shown  to 
a  greater  or  less  degree  by  all  organisms,  and  constitutes 
a  fundamental  condition  of  self-preservation;  tyi)ically 
if  the  organism  is  deprived  of  any  substance  or  condition 
necessary  for  maintenance,  its  reactivity  and  behavior 


30    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

are  altered  in  a  manner  tending  to  compensate  or  remove 
the  deficiency.  Thus  hunger  is,  physiologically  speaking, 
increased  reactivity  to  food  materials ;  thirst  is  increased 
reactivity  to  water ;  the  respiratory  center  of  vertebrates 
increases  its  rhythm  as  CO2  accumulates  in  the  blood; 
when  the  oxygen  in  the  water  is  decreased,  the  gill-cilia 
of  the  fresh-water  clam  beat  more  vigorously/  These 
and  many  other  instances  illustrate  the  manner  in  which 
a  physiological  deficiency  may  itself  furnish  the  means 
of  setting  in  motion  some  physiological  mechanism  which 
remedies  the  deficiency.^  The  end-effect  of  all  such 
regulatory  responses  is  to  further  the  persistence  of  the 
organism  in  its  environment.  As  already  mentioned, 
the  term  adaptive  is  usually  applied  to  those  special 
peculiarities  of  structure  and  activity  by  which  the 
organism  is  automatically  conserved  in  spite  of  environ- 
mental change;  hence,  from  the  present  generalized 
point  of  view  any  active  adaptation  may  be  regarded 
as  a  special  kind  of  regulation.  It  is  evident  that  all 
such  regulations  are  based  upon  a  highly  developed 
irritability;  this  fundamental  property  of  irritability, 
therefore,  controls  all  of  the  active  relations  between 
organism  and  environment,  including  the  interchange  of 
material  and  energy  which  is  the  essential  feature  of  such 
relations. 

SPECIFIC  CHARACTERS  OF  ORGANISMS 

The  constructive  metabolic  processes  which  build  up 
the  living  system  involve  the  synthesis  of  a  multiplicity 
of  new  chemical  compounds  from  the  food  materials  and 

^  Cf.  Babak,  Z.  allg.  Physiol.,  XV  (1913),  184. 

2  In  Pfliiger's  aphorism,  in  living  organisms  "the  cause  of  the  need 
is  the  cause  of  the  satisfaction  of  the  need." 


GENERAL  CHARACTERS  OF  LIVING  OR^^VIS.MS       i 

other  substances  (oxygen,  salts,  water)  furnished  by  the 
environment.  Of  these  synthesized  compounds  the 
most  individualized  and  specific  are  the  proteins.  These 
compounds,  characteristically  colloidal  in  their  physical 
properties,  constitute,  together  with  certain  other 
materials,  chiefly  lipoid,  the  relatively  stable,  soHd,  or 
permanent  (structural)  portion  of  the  protoplasmic 
complex. 

It  is  significant  that  the  chief  structure-forming 
compounds  should  be  at  the  same  time  those  which  are 
chemically  the  most  specific.  Specific  form  and  structure 
are  the  most  obvious  peculiarities  of  the  living  organism; 
hence  species  are  usually  distinguished  by  their  structural 
characters.  It  is  to  be  remembered,  however,  that  the 
chemical  and  physiological  characters  are  equally 
constant  and  definite,  and  must  be  included  in  the 
complete  characterization  of  any  species.  The  essential 
fact,  requiring  physiological  explanation,  is  that  each 
individual  animal  or  plant  resembles,  structurally, 
chemically,  and  physiologically  other  indi\'iduals  of  the 
same  species,  while  differing  from  those  of  other  species. 
As  already  indicated,  the  physiological  basis  of  this 
specificity  is  to  be  sought  in  the  specific  nature  of  the 
chemical  processes  by  which  the  organism  is  synthesized. 
We  find  in  fact  that  a  chemical  specificity,  corresponding 
to  the  specificity  of  the  organism  as  a  whole,  is  exhibited 
by  its  constituent  proteins,  and  api)arently  by  these 
compounds  alone.  The  other  chief  biochemical  com- 
pounds (carbohydrates,  lipins)  are  chemically  identical 
in  widely  difi"ering  species,  while  the  proteins  vary  in 
their  detailed  chemical  character  from  species  to  species. 
Apparently  each  native  protein  has  a  special  comi)osition 


32  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

and  stereo-chemical  configuration,  by  which  it  is  dis- 
tinguished from  the  corresponding  proteins  of  even 
nearly  related  species.  This  general  fact  of  an  associa- 
tion between  specific  chemical  composition  and  specific 
organic  structure  indicates,  together  with  other  evidence, 
that  the  specific  chemical  characters  of  the  structural 
proteins  of  any  organism  determine,  in  a  manner  which 
cannot  be  defined  in  detail  at  present,  its  specific  pecu- 
liarities as  an  organic  species/  Apparently  this  chemical 
specificity  determines  the  more  intimate  protoplasmic 
structure,  and  hence  indirectly  the  protoplasmic  activi- 
ties, chemical  and  other,  which  are  the  correlative  of 
that  structure  and  determine  ultimately  the  physiological 
and  other  peculiarities  of  the  species. 

The  problem  of  the  conditions  of  specific  form- 
determination  in  organisms  has  its  special  physiological 
aspects;  but  on  the  purely  physical  side  its  closest 
affiliations  are  with  the  problem  of  the  relations  between 
the  chemical  constitution  of  compounds  and  their 
crystalline  or  other  molar  structure.  When  similar 
molecules  unite  to  form  larger  molar  aggregates,  definite 
regularities  of  form  and  structure  usually  make  their 
appearance;  this  is  especially  true  when  substances 
separate  from  solution  to  form  crystals;  the  axes  and 
angles  of  the  crystal  form  are  an  index  of  the  orientation 
which  the  molecules  assume  as  the  aggregate  is  built 
up,  and  of  the  linear  proportions  of  the  molecules. 
In  most  solid  compounds  this  association  of  structural 
specificity    with    chemical    specificity    can    be    readily 

^  Cf.  Loeb's  recent  discussion  in  his  Organism  as  a  Whole  from  a 
Physico-Chemical  Viewpoint,  New  York  (191 6),  chap,  iii,  "The  Chemical 
Basis  of  Genus  and  Species." 


GENERAL  CHARACTERS  OF  LR'IXG  ORdAXISM.-. 


oo 


demonstrated;  i.e.,  each  compound  has  a  definite  and 
characteristic  crystalline  form,  which  is  similar  for 
compounds  of  similar  chemical  confi'^uration  (law  of 
isomorphism).  In  colloidal  comi)ounds  like  i)r()teins, 
crystals  are  less  easily  produced,  but  under  appr()j)riate 
conditions  many  of  these  compounds  can  be  crystallized, 
and  it  is  then  found  that  corresponding  or  homologous 
proteins  from  different  species  form  crystalline  aggregates 
which  differ  characteristically  in  their  specific  form- 
characters.  Specificity  of  crystalline  form  has  been 
demonstrated  most  clearly  in  the  case  of  the  hemoglo- 
bins; i.e.,  the  haemoglobin  crystals  of  the  domestic  cat 
differ  in  a  definite  and  constant  manner  from  those  of 
other  species  of  the  same  family,  and  in  different  verte- 
brates a  general  correlation  between  similarity  of  cr}'stal 
form  and  nearness  of  relationship  can  be  recognized.* 
Such  facts  indicate  that  as  the  molecules  unite  in  the 
process  of  crystallization  to  form  larger  aggregates, 
structures  are  built  up  having  definite  moq)hoi()gical 
characters  w^hich  are  determined  by  the  special  configura- 
tion of  the  haemoglobin  molecule.  The  growing  crystal 
mass  takes  on  definite  form  characters,  like  the  growing 
germ.  We  may  assume  that  in  the  living  cell,  as  it  grows 
and  differentiates,  similar  conditions  determine  the 
physical  state  assumed  by  those  proteins  which  are  laid 
down  as  microscopic  aggregates  or  deposits  to  form  the 

'  Cf.  Reichert  and  Brown,  "The  Crystallography  of  IIx«mcKlobins," 
Carnegie  Institution  Publication  No.  ii6,  Washington  (iqoq);  also 
Reichert's  paper,  "The  Germ  Plasm  as  a  Stcrcochemic  System,"  Science, 
XL  (1914),  649.  Nuttall's  work  with  precipitin  reactions  demonstrates 
a  similar  correlation  between  the  chemical  specificity  of  proteins  and 
blood  relationship.  (Xuttall,  Blood  Immunity  and  Blood  Relationships, 
Cambridge  University  Press^[i904l.) 


34    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

protoplasmic  structures;  in  such  a  case  a  specific  proto- 
plasmic and  ultimately  a  specific  cellular  structure 
would  be  produced,  corresponding  to  the  specific  constitu- 
tion of  the  structure-forming  compounds. 

The  general  nature  of  the  relation  between  stereo- 
chemical configuration  and  crystalline  form  is  best 
illustrated  by  Pasteur's  classical  investigations  on  the 
tartrates.  The  characteristic  spatial  arrangement  of  the 
atoms  in  the  d-tartrate  molecule  is  evidently  what 
determines  the  production  of  the  specifically  formed 
asymmetric  crystals  of  this  compound.  Similarly  con- 
stituted molecules  have  a  tendency  to  segregate,  hence 
the  dextro-  and  laevo-groups  in  the  solution  of  the 
racemic  salt  unite  separately  to  form  separate  crystals. 
The  importance  of  such  conditions  in  the  chemical 
processes  of  protoplasm  is  illustrated  in  the  characteristic 
relations  existing  between  the  stereo-configuration  of 
asymmetric  compounds  and  their  assimilability,  ferment- 
ability  and  physiological  action.  The  possibilities  of  a 
specificity  based  on  stereo-chemical  configuration  are  at 
a  maximum  in  compounds  like  proteins,  built  up  of 
chains  of  asymmetric  amino-acids.  As  we  have  seen, 
chemical  specificity  implies  structural  specificity  in  the 
aggregate  formed  from  such  molecules. 

As  is  well  known,  the  chief  proofs  of  the  chemical 
specificity  of  closely  related  proteins  are  derived  from 
immunological  and  related  phenomena.  Antigenic  prop- 
erties are  apparently  confined  to  proteins,  and  this 
peculiarity  is  of  fundamental  importance  in  relation  to 
the  whole  problem  of  the  conditions  of  specific  synthesis 
in  organisms.  When  a  foreign  protein  is  introduced  into 
the  tissue-media  of  higher  animals,  one  of  its  physiological 


GENERAL  CHARACTERS  OF  LIVING  ORGANISMS    35 

effects  is  to  alter  constructive  metabolism  in  the  cells 
of  the  organism  in  a  definite  manner  so  as  to  give  rise 
to  other  compounds  (apparently  also  protein)  of  related 
or  complimentary  configuration.  These  new  com- 
pounds, anti-bodies,  form  specific  chemical  unions  with 
the  antigens,  and  hence  may  serve  as  a  means  of  identify- 
ing the  latter  or  of  distinguishing  between  nearly  related 
proteins,  as  in  the  precipitin  and  anaphylaxis  reactions. 
The  living  protoplasm  responds  to  the  presence  of  the 
antigen  by  synthesizing  a  compound  of  similar  or 
complementary  configuration;  and  this  chemical  resem- 
blance is  what  determines  the  intimacy  and  specificity 
of  union  in  the  antigen-anti-body  reaction.  The 
anaphylactic  guinea-pig  is  in  fact  the  most  sensitive 
means  at  our  disposal  for  distinguishing  between  proteins 
of  nearly  related  composition.^ 

It  is  evident  that  such  phenomena  have  a  most 
important  bearing  on  the  question  of  the  basis  of  organic 
specificity.  They  indicate  not  only  that  the  synthesis 
of  specific  compounds  by  living  protoplasm  is  determined 
by  the  presence  of  other  specific  compounds,  a  fact  of 
general  application  in  the  theory  of  growth  processes, 
but  also  that  the  specific  syntheses  characteristic  of  a 
species  may  be  modified  under  the  influence  of  compounds 
having  a  different  configuration  from  those  normall\- 
present.  The  indications  from  precipitin  and  other 
tests  are  that  the  chemical  resemblance  between  the 
corresponding  proteins  of  difi'erent  species  is  greatest  when 
the  biological  relationship  is  closest — when  the  species  are 
structurally  and  physiologically  most  closely  simihir — 
and  in  general  decreases  as  the  organic  diflcrence  increases. 

*  Cf.  S,  Flexner,  Science,  LII  (1920),  615. 


36    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

The  general  conclusion  seems  therefore  justified  that 
the  specific  biological  characters  of  an  animal  or  plant 
depend  ultimately  upon  the  specific  chemical  characters 
of  its  proteins.  The  developing  germ,  or  the  growing 
and  metabolizing  organism,  builds  up  proteins  of  specific 
constitution,  and  these,  since  they  determine  the  specific 
structural  characters- — ^with  the  correlative  physiological 
activities^ — of  the  organism,  form  the  basis  of  its  biological 
specificity  or  special  singularity  as  an  organic  species. 
A  fundamental  problem,  therefore,  relates  to  the  condi- 
tion determining  the  synthesis  of  proteins  of  its  own 
specific  type  by  each  form  of  protoplasm.  This  problem 
is  as  yet  unsolved.  Apparently  the  presence  of  proteins 
of  a  certain  composition  and  configuration  promotes  or 
''catalyzes"  the  formation  of  proteins  of  similar  or  com- 
plementary configuration.  A  general  condition  compar- 
able with  autocatalysis^  thus  determines  the  specific  char- 
acter of  the  protoplasmic  syntheses,  but  such  a  statement 
merely  defines  the  problem  without  solving  it.  The 
problem,  however,  cannot  be  solved  before  it  is  clearly 
defined,  and  its  solution  would  unquestionably  represent 
a  great  advance  in  biological  knowledge,  since  it  would 
involve  the  solution  of  the  fundamental  problems  of 
growth  and  heredity. 

There  is  some  evidence  of  an  identity,  or  at  least 
close  chemical  resemblance,  between  the  specific  proteins 
of  adult  tissues  or  organs  and  corresponding  or  repre- 

^  For  the  comparison  of  organic  growth  with  autocatalysis  cf .  J 
Loeb,  Biochem.  Zeitschrift,  II  (1906),  41;  T.  B.  Robertson,  Arch.  Ent- 
wicklungsniech.,  XXIV  (1908),  581;  Wfg.  Ostwald,  Roux's  Vortrdge  und 
Anfsatse,  V  (1908).  Chodat  made  a  similar  comparison  for  plant  growth 
in  1905  (cf.  D'Arcy  Thompson's  Growth  and  Form,  Cambridge  Uni- 
versity Press  [1917],  p.  132). 


\ 


GENERAL  CHARACTERS  OF  LIVING  ORGANISMS    37 

sentative  proteins  in  the  germ  cells.  Guyer'  has  recently 
found  that  the  germ  cells  of  rabbits  which  ha\e  been 
injected  with  anti-lens  serum  (formed  by  immunization 
in  fowds  injected  with  crushed  rabbit  lenses)  are  so 
modified  as  to  give  rise  in  development  to  rabbits 
having  defective  lenses  and  otherwise  abnormal  eyes. 
These  defects  are  transmitted  hereditarily  by  either  ova 
or  spermatozoa  through  several  generations.  Since 
anti-bodies  attach  themselves  to  proteins  of  correspond- 
ing configuration,  these  observations  are  evidence  of  the 
presence  of  the  specific  lens  proteins  (or  proteins 
closely  corresponding)  in  the  germ  cells.  Results  of  an 
analogous  kind  recently  reported  by  Detlefsen  and 
Grifiith  may  possibly  have  a  similar  significance;  rats 
which  had  been  subjected  to  prolonged  rotation  gave 
rise  to  offspring  showing  characteristic  defects  in  equi- 
librium and  tendency  to  circus-movements,  and  those 
abnormalities  were  also  heritable.^ 

While  it  is  difficult  to  believe  that  all,  or  even  more 
than  a  very  few,  of  the  proteins  in  the  adult  body  are 
represented  by  corresponding  proteins  in  the  germ,  yet 
it  seems  not  improbable  that  there  may  exist  some 
correspondence  of  a  general  kind  between  the  chemical 
organizations  of  adult  and  germ,  analogous  to  or  parallel- 
ing the  general  morphological  correspondence  which 
Conklin's   work^   has   demonstrated   between    the   eggs 

^  Guyer  and  Smith,  Journal  of  Experimental  Zoology,  XX\I  (191 8), 
65,  and  XXXI  (1920),  171.  Cf.  also  American  Xaturalist,  LV  (io-mV 
97,  and  LVI  (1922),  80. 

2  Cf.  Griffith,  Science,  LVI  (1922),  676. 

3Cf.  Conklin,  Heredity  and  Environment  in  the  Dadopment  of 
Man,  Princeton  University  Press  (1918);  also  his  paper,  "The  Share 
of  Egg  and  Sperm  in  Heredity,"  Proceedings  of  the  National  Academy  oj 
Science,  HI  (191 7) >  loi- 


SS    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

and  the  larval  stages  in  certain  animals.  That  is,  certain 
proteins  with  a  basic  or  fundamental  relation  to  the 
organization  of  the  species  may  be  chemically  identical 
in  adult  and  germ;  and  they  may  even  be  distributed 
spatially  in  a  similar  way  in  both;  e.g.,  with  reference 
to  the  main  axes.  In  this  sense  a  chemical  continuity 
between  germ  and  adult  may  exist,  corresponding  to  the 
morphological  continuity.  At  present,  however,  we 
are  completely  ignorant  regarding  the  details  of  this 
correspondence  and  can  only  await  the  results  of  further 
investigation. 

EXPERIMENTAL  MODIFICATIONS  OF  GROWTH 
AND  HEREDITY 

If  the  metabolic  production  of  proteins  of  specific 
configuration  constitutes  the  essential  chemical  basis  of 
growth  and  development,  it  must  also  form  the  basis  of 
heredity,  since  by  ''heredity"  is  meant  not  a  separate 
phenomenon  but  simply  the  similarity  of  the  constructive 
or  developmental  process  in  the  successive  generations  of 
a  particular  organic  species.  We  may  therefore  regard  the 
factors  of  growth  as  identical  with  the  factors  of  heredity, 
and  apply  the  same  type  of  physiological  analysis  in 
both  cases. 

We  find  experimentally  that  while  under  normal 
conditions  development  follows  a  highly  definite  and 
constant  course  in  each  species,  it  can  be  altered  in  a 
definite  manner  by  various  procedures;  and  a  large 
part  of  experimental  embryology  is  concerned  with 
modifying  the  growth  processes  in  the  germ  or  embryo 
and  thus  controlHng  the  rate  and  character  of  develop- 
ment.    In  this  manner  it  has  been  shown  that  constancy 


GENERAL  CHARACTERS  OF  LIVING  ORGANISMS    39 

of  development  in  any  particular  species  requires 
constancy  in  the  external  conditions.  For  example,  the 
developing  sea-urchin  larva  forms  a  skeleton  of  a  charac- 
teristic and  often  complex  design  in  sea  water  and  in 
artificially  balanced  media  containing  the  chief  salts 
of  sea  water  together  with  some  sodium  carbonate; 
the  formation  of  this  skeleton  causes  the  larva  to  assume 
the  triangular  and  long-armed  shape  characteristic  of 
the  pluteus  stage.  But  if  the  carbonate  is  omitted 
from  the  medium,  the  skeleton  fails  to  form,  and 
development  does  not  proceed  beyond  the  gastrula  stage. ^ 
The  special  form  of  the  skeleton  is  said  to  be  ''inherited"; 
this  experiment  shows,  however,  that  it  is  dependent  on 
the  presence  of  carbonate  quite  as  much  as  on  the 
presence  of  special  determinants  in  the  germ. 

Such  an  example  show^s  further  that  constancy  in 
the  normal  sequence  of  growth  processes  is  the  essential 
condition  for  the  manifestation  of  heredity;  it  also 
illustrates  the  composite  nature  of  the  physiological 
factors  determining  the  production  of  any  adult  form- 
character;  in  all  cases  the  co-operation  of  definite 
''internal"  and  "external"  factors  is  necessary  to  yield 
the  final  result.  Many  cases  are  also  known  where 
development  is  altered  in  a  definite  manner  by  the  addi- 
tion of  special  growth-modifying  substances;  a  well- 
known  example  of  such  influence,  exerted  by  a  simple 
inorganic  substance,  is  the  production  of  cyclopia  in 
fishes  by  increasing  the  magnesium  content  of  sea 
water  ;^      other    substances     and     conditions     (alcohol 

'  J.  Loeb,  American  Journal  of  Physiology,  111  (1900),  44i- 
^Stockard,  Arch.  Eulwkkl.  Organ.,  XXTTT  (1907),  249;   Jourual  of 
Experimental  Zoology,  VI  (1909),  285. 


40    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

anaesthetics,  cyanide,  cold)  have  a  similar  effect.^ 
These  substances  hinder  or  suppress  the  growth  of  the 
anterior  region  of  the  forebrain  between  the  optic 
vesicles  so  that  the  latter  tend  to  approximate  and 
coalesce,  producing  a  single  instead  of  a  double  structure.^ 
The  production  of  exogastralae  from  sea-urchin  blastula? 
by  adding  lithium  chloride  to  the  sea  w^ater  is  a  similar 
instance;  in  this  case  the  endoderm  grows  outward 
instead  of  inward.^  The  transition  is  direct  from  such 
simple  cases  of  artificial  chemical  control  of  development 
to  the  cases  where  various  developmental  processes  occur 
normally  under  the  control  of  special  chemical  substances 
produced  by  the  organism  itself;  the  influence  of  hor- 
mones illustrates  such  cases;  metamorphosis  (in  tad- 
poles), the  growth  of  the  skeleton,  and  the  production 
of  sexual  characters  are  thus  determined. 

In  general  any  condition  affecting  the  rate  or  character 
of  the  formative  metabolic  reactions  has  a  corresponding 
influence  on  growth  and  development.  Such  conditions 
include  the  influence  of  physical  agents  like  electricity, 
light,  temperature,  contact.  It  is  significant  that  the 
term  ''irritability"  is  applied,  especially  in  plant  physi- 
ology, to  the  susceptibility  of  growth  processes  to  such 
modifying  influences;  in  such  cases  the  organism  ''re- 
sponds" by  changing  its  rate  or  manner  of  growth.  Any 
such  response  implies  a  corresponding  modification  in  con- 
structive metabolism;    hence   such  facts  show  that  re- 

^  Cf .  Stockard,  American  Journal  of  Anatomy,  X  (1910),  369; 
McClendon,  American  Journal  of  Physiology,  XXIX  (191 2),  289. 

^  Cf.  the  discussion  in  Child's  Origin  and  Development  of  the  Nervous 
System,  pp.  36  ff. 

3  Cf.  Herbst,  Z.  wiss.  Zool.,  IV  (1892),  446;  Mitteilungen  zool. 
Sta.  Neapel,  XI  (1893),  136. 


GENERAL  CHARACTERS  OF  LI\ING  ORGANISMS    41 

sponses  involving  metabolic  synthesis  are  called  forth 
under  the  same  conditions  as  the  other  more  familiar 
types  of  response,  such  as  muscuLar  contraction  in 
animals,  which  depends  more  directly  ui)()n  processes  of 
metabolic  breakdown. 

The  importance  of  the  relations  existing  between 
normal  growth  and  the  normal  physiological  activity  of 
the  organism  has  been  hitherto  insufficiently  recognized. 
Probably  the  main  reason  for  this  is  that  in  the  egg  and 
early  embryo  the  development  of  any  organ  up  to  a 
certain  stage  necessarily  precedes  its  functional  activity; 
often,  in  fact,  development  is  complete  before  there  is  any 
possibility  of  function  (generative  organs,  many  muscular 
mechanisms).  In  many  other  cases,  however,  normal 
physiological  activity  is  a  prerequisite  for  normal 
growth  and  development.  Inactivity  means  lowered 
or  subnormal  metabolism,  and  this  involves  subnormal 
growth;  frequently,  when  physiological  activity  is 
subnormal,  metabolic  construction  lags  behind  destruc- 
tion, and  regression  or  atrophy  (/'disuse-atroi)hy") 
results.  The  need  of  activity  for  normal  growth  is  most 
evident  in  the  adult  stages  of  higher  organisms,  and  is 
especially  well  shown  in  intermittently  active  tissues 
like  voluntary  muscle,  where  increased  activity  leads  to 
increased  growth,  as  shown  in  the  effects  of  exercise. 
while  disuse  is  followed  by  regression  more  or  less 
complete.  Other  tissues  show  similar  conditions;  the 
removal  of  one  kidney  is  followed  by  increase  in  the 
size  of  the  other,  in  correlation  with  the  enforced  increase 
of  activity;  and  valvular  insufficiency  in  the  heart  leads 
to  muscular  enlargement.  Such  cases  of  C(Mni)ensatory 
hypertrophy  are  apparently  an  example  of  the  above- 


42     PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

cited  general  rule,  and  indicate  clearly  that  the  physico- 
chemical  conditions  determining  functional  activity  are 
in  close  relation  to  those  determining  metabolic  synthesis 
and  growth. 

Claude  Bernard  has  pointed  out  that  in  any  living 
system  a  relation  of  this  kind  must  exist  if  the  system 
is  to  persist  and  retain  its  normal  properties  under 
varying  conditions  of  activity/  All  activity  involves  a 
certain  breakdown  of  organized  structural  material,  as 
well  as  of  energy-yielding  compounds  like  sugar;  hence 
a  return  to  the  normal  or  resting  condition  after  stimula- 
tion requires  that  compensatory  or  constructive  processes 
should  be  set  in  motion  by  the  same  condition  that  calls 
forth  the  destructive  or  energy-yielding  activity. 

The  general  metabolism  of  any  Living  system  repre- 
sents an  ordered  combination  of  constructive  and 
destructive  processes;  the  living  condition  always 
involves  metabolic  construction;  as  Bernard  expresses 
it,  "synthesis  is  life,"  even  during  rest.  Hence  the  rate 
of  metabolic  construction  is  to  be  recognized  as  under 
the  same  kind  of  control  as  the  rate  of  destruction;  i.e.,  of 
energy-production  or  normal  activity.  Growth  processes 
are  therefore  modified  by  any  condition  (cold,  poisons, 
H-ion  concentration,  salts,  anaesthetics)  which  alters  the 
general  activity  of  the  living  cell.  The  growth  of  the 
embryo  can  be  temporarily  arrested  by  anaesthetization; 
the  same  is  true  of  seedlings  and  dividing  cells.''     Such 

^  Claude  Bernard,  Lemons  stir  les  phenomenes  de  la  vie,  I,  127. 

^  Bernard  describes  the  anaesthesia  of  seedlings  and  embryos  (La 
Science  Experimentale,  Paris  [1890],  p.  224).  For  a  study  of  anaesthesia 
of  cell-division,  see  my  article  in  Journal  of  Biological  Chemistry,  XVII 
(1914),  121. 


GENERAL  CHARACTERS  OF  LIVING  ORGANISIVrS    43 

facts  illustrate  the  unitary  character  and  control  of  the 
metabolic  processes  underlying  the  various  vital  manifes- 
tations; they  show  that  growth  and  development  are 
controlled  by  the  same  conditions  as  the  other  forms  of 
protoplasmic  activity.  Hence  stimulation  is  a  concep- 
tion which  is  applicable  to  growth  processes  in  the  same 
sense  as  to  muscular  or  nervous  activity. 

Constructive  metaboHsm  thus  varies  with  the  general 
physiological  activity  of  the  living  system;  and  this 
latter  activity  is  determined  largely  by  the  external 
agents  which  act  upon  or  ^'stimulate"  the  protoplasm. 
The  general  property  of  ''irritabihty"  thus  implies  not 
only  the  ability  of  the  protoplasmic  system  to  carry 
out  definite  reactions  in  response  to  stimuli  but  also 
the  ability  to  vary  its  constructive  metabolism  in 
correlation  with  the  rate  or  degree  of  the  energy -yielding 
or  destructive  processes.  Restitution,  compensatory 
growth,  recovery  from  injury,  or  fatigue  and  apparently 
the  normal  recovery  of  the  irritable  state  after  stimulation 
are  different  manifestations  of  this  constiucti\'c  process. 

GENERAL  FEATURES  OF  STIMULATION  PROCESSES 

In  general,  the  term  '^irritability,"  as  used  in  physiol- 
ogy, designates  the  universal  property  of  living  matter 
by  which  the  chemical  or  other  activities  of  the  living 
system  change,  in  some  specific  way,  in  response  to 
changes  in  the  surroundings.  We  say  ''change  in  some 
specific  way",  i.e.,  in  a  manner  distinctive  of  the  living 
system,  in  order  to  separate  true  cases  of  stimuhition 
from  cases  where  the  chemical  or  other  processes  occurring 
in  the  protoplasm  are  changed  as  a  direct  consequence 
of  non-vital   factors.     For  example,   within   the  usual 


44    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

physiological  range  (5°-4o°)  a  rise  of  temperature  of 
io°  more  than  doubles  the  rate  of  most  chemical  reactions 
(Qio  2-3);  this  rule  applies  to  many  processes  which, 
though  occurring  within  the  living  system,  have  in  them 
nothing  that  is  specifically  vital;  thus  the  rate  of  hydrol- 
ysis in  the  digestive  tract,  the  rate  of  consumption  of 
oxygen  or  evolution  of  CO2  by  living  cells,  and  the  rate 
of  autolysis  in  dead  cells  are  all  accelerated  to  about 
the  same  degree  by  a  given  rise  of  temperature;  the 
same  is  true  of  chemical  reactions  in  non-living  systems; 
e.g.,  the  hydrolysis  of  sucrose  by  acid.  Such  accelera- 
tions are  not  instances  of  stimulation  in  the  physiological 
sense;  true  stimulation  is  illustrated  only  when  the 
organism,  cell,  or  other  living  system  makes  a  response 
whose  characteristics  can  be  explained  only  by  reference 
to  the  special  peculiarities  of  the  system  as  living. 
Thus  a  muscle  can  be  mechanically  subdivided  by 
scissors,  and  the  purely  mechanical  action  is  the  same  in 
the  living  as  in  the  dead  muscle;  but,  in  addition,  the 
former  contracts,  i.e.,  exhibits  its  characteristically  vital 
response.  Or  a  living  unfertilized  starfish  egg  or  frog's 
egg  mechanically  treated  in  an  appropriate  way  begins 
a  sequence  of  cell-divisions;  the  same  result  follows 
when  a  starfish  egg  is  kept  at  35°  for  2  minutes,  or  treated 

with  —  butyric  acid  solution  for  a  similar  period. 
200 

The  change  in  the  behavior  of  the  living  system  under 

a  given  stimulating  condition  is  normally  a  constant  one, 

but  the  special  nature  of  this  change  is  determined  by 

the   specific   organization   or   'inherited"    character   of 

the  system,  as  well  as  by  its  physiological  state  at  the 

time.     Hence  the  same  change  of  conditions  acting  as  a 


GENERAL  CHARACTERS  OF  LIVING  ORGANISMS    45 

stimulus  may  produce  entirely  different  effects  upon 
different  irritable  systems,  or  upon  the  same  system  at 
different  times.  For  example,  the  same  intensity  of 
light  will  repel  one  group  of  animals,  and  attract  another; 
mechanical  treatment  may  arouse  increased  activity  in 
one  motor  organ  (a  muscle)  and  inhibit  it  in  another 
(the  swimming  plate  of  a  ctenophore).  The  case  just 
cited  is  interesting  as  illustrating  another  general  feature 
in  the  behavior  of  irritable  systems;  the  swimming  plates 
of  Mnemiopsis  or  Eucharis  beat  rhythmically  with 
considerable  regularity,  but  instantly  cease  movement 
when  mechanically  stimulated  in  the  presence  of  sufficient 
Ca  salts;  e.g.,  in  sea  water  or  artificial  media  containing 
calcium;  but  in  similar  media  containing  no  calcium, 
mechanical  treatment  entirely  fails  to  inhibit  the  move- 
ment, and  on  the  contrary  accelerates  it.^  This  instance 
shows  that  the  same  external  change  of  condition  may 
produce  different  effects  in  the  same  tissue  according  to 
its  physiological  state  at  the  time;  under  one  condition 
there  is  an  inhibitory,  under  another  an  acceleratory 
response.  Electrical  stimulation  of  the  nerve  supplying 
a  voluntary  muscle  causes  the  latter  to  contract;  but 
the  same  stimulus  applied  to  the  cardiac  branch  of  the 
vagus  nerve  inhibits  contraction. 

Such  examples  illustrate  the  distinction  between  the 
stimulating  effect  of  an  agent  or  change  of  condition 
upon  an  irritable  living  system,  and  the  ch'rect  effect 
which  it  produces  by  its  purely  physical  or  chemical 
action  upon  the  system.  Superposed  upon  and  sequent 
to  the  direct  physico-chemical  effect  is  the  special  or 
physiological  effect,  the  nature  of  which  depends  on  the 

'  R.  S.  Lillie,  American  Journal  oj  Physiology,  XXI  (1908),  zoo. 


46  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

specific  vital  properties  of  the  system.  The  given 
physico-chemical  change  calls  forth  or  occasions  a 
definite  change  of  activity  peculiar  to  the  system. 
The  physiological  problem  of  stimulation  has  reference  to 
the  physical  and  chemical  nature  of  the  conditions 
under  which  this  specific  vital  reaction  is  called  forth. 

Only  a  special  acquaintance  with  a  given  living 
system  or  organism  can  enable  us  to  predict  what  its 
behavior  will  be  under  a  given  stimulating  condition. 
Irritability  as  such,  however,  is  a  property  which  is 
manifested  under  comparatively  uniform  conditions  in 
all  organisms;  i.e.,  the  tendency  to  respond  to  certain 
kinds  of  physical  change  is  very  widely  distributed,  if 
not  universal.  Such  responsiveness  is  a  general  character 
of  living  matter  and  is  largely  independent  of  special 
features  of  structure  and  organization.  Thus  apparently 
all  forms  of  protoplasm  are  influenced  in  their  activity 
by  the  electric  current;  in  many  cases — nerves,  certain 
receptors,  muscles — very  weak  currents  are  sufficient 
for  stimulation;  i.e.,  induce  a  sudden  and  profound 
change  in  the  activity  of  the  system;  in  other  cases  the 
sensitivity  to  the  current  is  less  and  the  response  is 
more  gradual.  The  electrical  sensitivity  of  living  matter 
is  in  fact  one  of  its  most  characteristic  peculiarities. 
Evidently  there  is  some  feature  of  protoplasmic  structure 
or  organization,  common  to  all  cells  and  organisms, 
that  renders  all  responsive  to  electricity,  although  in 
varying  degrees.  The  same  is  true  (though  perhaps  less 
universally)  of  mechanical  influences  or  change  of 
temperature.  Chemical  sensitivity  is  also  universal; 
since  all  living  matter  depends  for  its  existence  upon  the 
incorporation    and    transformation    of    the    assimflable 


GENERAL  CHARACTERS  OF  LIVING  ORGANISMS    47 

materials  present  in  the  surroundings,  the  existence  of  a 
highly  developed  responsiveness  to  the  external  chemical 
conditions  is  to  be  expected.  It  is  especially  remarkable 
that  certain  groups  of  compounds — the  lipoid-solvent  or 
anaesthetizing  group — have  a  similar  reversible  dejjres- 
sant  action  on  protoplasmic  activities  in  all  organisms, 
from  bacteria  to  higher  plants  and  animals. 

We  may  class  therefore  as  universal  properties  of 
protoplasm:  (i)  electrical  sensitivity,  and  (2)  sensitivity 
to  the  presence  of  special  chemical  substances  in  the 
surroundings.  In  studying  the  problem  of  the  conditions 
of  stimulation  we  are  thus  brought  to  consider  more 
especially  the  reactions  of  living  matter  to  electricity 
and  to  chemical  substances  in  the  environment.  The 
fundamental  or  essential  features  of  protoplasmic 
structure  and  composition  must  be  those  which  determine 
the  special  responsiveness  to  influences  of  these  two 
kinds. 


CHAPTER  IV 

GENERAL  PECULIARITIES  OF  PROTOPLASM  AS 
A  PHYSICAL  SYSTEM 

In  considering  the  general  peculiarities  of  living  proto- 
plasm, it  is  essential  to  recognize  that  its  characteristic 
properties  and  activities  depend  upon  features  of  composi- 
tion and  structure  which  are  kept  in  permanent  existence 
only  through  a  continued  process  of  compensation, 
consisting  in  the  metabolic  construction  of  new  and 
specific  compounds  to  replace  those  broken  down  or  lost 
in  vital  activity.  Without  this  continual  automatic 
renewal  and  repair  the  system  is  an  unstable  one  and 
cannot  persist.  Physical  diffusion  and  the  normal 
chemical  processes  of  oxidation  and  hydrolysis  all  act 
toward  producing  a  disintegration  of  the  system;  these 
effects  are  well  seen  in  experiments  on  autolysis;  the 
dead  cell  digests  itself  and  its  soluble  constituents  diffuse 
into  the  surroundings.  During  life  the  structural  and 
chemical  integrity  of  the  system  is  maintained  by  means 
of  its  continued  synthetic  activity;  the  cessation  of  this 
activity  is  the  essential  change  in  death. 

This  general  conception  of  living  matter,  as  a  system 
which  holds  its  own  through  a  balance  of  constructive 
and  disintegrative  processes,  is  fundamental  in  physi- 
ology. Other  systems  exhibiting  an  analogous  type  of 
equilibrium,  i.e.,  between  constitutive  and  disintegrative 
processes,  are  of  frequent  occurrence  in  nature,  and  have 
been    classed    by    Ostwald    as    "stationary    systems.'" 

^  Ostwald,  Vorlesungen  iiher  Natiirphilosophie,  Leipzig  (1902), 
chaps,  xii,  xv. 

48 


PROTOPLASM  AS  A  PHYSICAL  b\.VlL.\l  49 

Whirlpools,  candle  flames,  waterfalls  are  exanii)li'S. 
Such  systems  also  exhibit  a  constant  confi^airalion,  and 
are  the  seat  of  special  activities,  in  which  access  of 
material  and  energy  from  without  balances  or  com- 
pensates the  tendency  to  disintegration  result  ins:  from 
their  own  activity  and  the  environmental  intluences. 
As  with  living  organisms,  their  integrity  depends  upon 
continual  and  balanced  interchange  with  the  surround- 
ings. A  further  general  resemblance  is  that  they  fre- 
quently possess  permanent  features  of  form  and  structure 
which  would  be  impossible  as  characters  of  systems  in 
static  equilibrium.  Such  types  of  equilibria — in  which 
opposed  active  processes  (rather  than  opposed  pressures, 
tensions,  or  potentials)  have  equal  and  opposite  resultant 
effects,  so  that  the  system  as  a  whole  retains  constant 
properties — are  often  called  ''dynamic"  or  ''kinetic'' 
equilibria.  The  possibilities  of  complex  structure,  and 
of  correspondingly  complex  activity,  are  at  a  maximum 
in  systems  of  this  constitution;  this  is  readily  seen  when 
we  contrast  a  fountain  with  still  water,  or  a  candle 
flame  or  fireworks  with  their  components  in  static 
equilibrium.  We  may  say  that  in  such  s)stems  the 
possibihties  of  the  fourth  or  time  dimension  arc-  added 
to  those  of  the  three  spatial  dimensions. 

Living  matter,  as  a  system  exhibiting  a  chnaiuic 
equilibrium  of  the  special  kind  already  indicated, 
exhibits  many  characteristic  peculiarities,  both  of 
structure  and  activity,  which  are  derived  from  this 
fundamental  feature  of  its  constitution.  All  living 
organisms  consist  largely  of  structures  which  would  not 
be  possible,  as  peniianencies,  if  the  structural  materials 
were  not  being  continually  fomied  and  deposited  in  such 


50    PROTOPLAS^nC  ACTION  AND  NERVOUS  ACTION 

a  way  as  to  offset  the  continual  breakdown;  and  these 
structures  subserve  or  render  actual  many  activities 
which  would  be  impossible  in  any  other  kind  of  system. 
In  general,  the  activities  which  are  most  characteristic 
of  living  as  distinguished  from  non-living  systems 
belong  in  this  class.  We  may  thus  understand,  on  the 
basis  of  the  general  properties  of  systems  in  stationary 
equilibrium,  the  possibility  of  the  existence  of  material 
systems  of  such  complex  structure  and  activity  as  living 
organisms.  The  power  of  regulation  exhibited  by 
stationary  systems,  i.e.,  of  returning  to  the  original 
state  after  disturbance,  is  one  of  the  chief  properties 
which  they  exhibit  in  common  with  living  systems. 
So  long  as  the  constitutive  processes  continue  in  action 
such  a  result  is  to  be  expected.  The  permanence  of 
such  delicate  structures  as  filaments,  films,  nerve  pro- 
cesses, and  the  other  finer  products  of  the  formative 
activity  of  protoplasm  depends  on  this  continual  auto- 
matic synthesis,  which  compensates  the  tendency  to 
physical  breakdown. 

When  any  irritable  organism  or  cell  responds  to 
stimulation,  the  energy  for  the  response  is  derived  from 
the  chemical  energy  of  the  protoplasmic  constituents, 
usually  from  the  oxidation  of  carbohydrates.  It  is 
clear  therefore  that  one  of  the  essential  effects  of  the 
stimulus  is  to  alter  the  rate  or  character  of  cell-metab- 
ohsm.  In  many  cases  this  effect  may  be  indirect;  e.g., 
in  the  voluntary  muscle  cell  a  large  part  of  the  heat- 
production  following  a  single  stimulus  succeeds  the 
contraction^   (Hill);    similarly  in  the  turgor-motors  of 

'  Cf.  A.  V.  HiU,  Journal  of  Physiology,  XLII,  XLIV,  XL VI,  XLVII 
(1911-13);  also  Ergebnisse  der  Physiol.,  XV  (1916),  340;  Physiological 
Reviews,  II  (1922),  310. 


PROTOPLASM  AS  A  PHYSICAL  SYSTEM  51 

plants  and  possibly  in  other  motile  organs.  But  in  all 
cases  the  work  performed  in  the  response  represents 
energy  derived  from  metabolic  breakdown,  although  this 
energy  may  act  in  the  intervals  between  stimulation  by 
developing  a  tension  or  turgor  which  is  released  only  at  the 
moment  of  stimulation.  A  fundamental  problem  thus 
arises  with  regard  to  the  general  nature  of  the  conditions  in 
living  matter  which  render  its  rate  of  chemical  reaction  so 
readily  alterable  by  physical  changes  in  the  system. 

The  most  significant  general  fact  is  that  it  is  only 
while  the  cell  is  living  that  its  rate  of  metabolism  is 
readily  and  quickly  changed  by  a  stimulating  condition. 
In  general,  also,  it  is  only  during  life  that  the  energy- 
yielding  forms  of  metabolism  have  a  high  rate  or  intensity; 
typically  COa-production,  heat-production,  and  con- 
sumption of  oxygen  decrease  greatly  at  death,  although 
they  may  not  cease  entirely.  One  of  the  most  remarkable 
peculiarities  of  living  protoplasm,  considered  as  a 
chemical  reaction-system,  is  that  its  chief  energ}-- 
yielding  reactions,  e.g.,  oxidation  of  sugar,  proceed 
rapidly  at  low  temperatures,  and  in  a  medium  which  is 
approximately  neutral.  To  produce  a  corresponding 
speed  of  reaction  in  vitro,  high  temperatures  or  strong 
reagents  are  required.  It  is  probable  that  the  conditions 
which  determine  the  susceptibiUty  to  stimulation  are 
the  same  as  those  which  are  responsible  for  the  hic:h 
velocity  of  the  energy-yielding  reactions.  The  nature 
of  these  conditions  is  imperfectly  understood  at  present; 
but  apparently  they  are  especially  fa\'orable  to  certain 
types  of  oxidation;   e.g.,  of  carbohydrates. 

The  indications  are  that  structural  rather  than  purely 
chemical    factors    are    of    chief    importance,    since    the 


52  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

oxidation-furthering  enzymes  (oxidases)  extractable  from 
the  cell  have  a  relatively  slight  influence  on  the  physi- 
ologically important  oxidations;  e.g.,  of  sugar.  We  may 
thus  regard  the  possession  of  a  certain  t}^e  of  structure, 
characteristic  of  the  living  state,  as  chiefly  responsible 
for  the  facility  with  which  chemical  reactions  proceed  in 
living  protoplasm,  as  well  as  for  their  modifiability 
under  stimulating  conditions.  The  synthetic  reactions 
appear  to  be  largely  dependent  upon  the  oxidations; 
this  is  indicated  by  the  importance  of  oxygen  for  growth 
processes,  as  well  as  by  various  other  facts,  although  the 
precise  nature  of  this  interdependence  is  not  understood 
at  present.  The  whole  problem  of  the  relations  between 
the  structure  of  protoplasm  and  its  chemical  activity 
is  one  of  fundamental  interest,  and  some  of  the  more 
general  facts  and  considerations  bearing  on  this  problem 
will  now  be  briefly  reviewed. 

CHEMICAL  REACTIVITY  OF  LIVING  MATTER  AS 
RELATED  TO  STRUCTURE 

All  Hving  matter  is  characterized  by  the  possession 
of  a  certain  structural  organization  or  permanent 
arrangement  of  components  which  is  essential  to  its 
normal  activity.  If  we  destroy  protoplasmic  structure 
by  heat,  mechanical  injury,  or  chemical  treatment,  the 
specific  metabolic  activity  of  the  system  and  its  respon- 
siveness to  stimulation  are  lost. 

In  general,  the  chemical  reactions  of  living  matter 
may  be  grouped  under  two  classes  according  to  their 
relation  to  protoplasmic  structure:  (A)  those  reactions 
which  continue  in  an  essentially  unaltered  manner  after 
the  "life"  of  the  ceU  has  been  destroyed;  e.g.,  in  cell- 


PROTOPLASM  AS  A  PHYSICAL  SYSTEM  c:^ 

extracts  or  in  the  residue  remaining  after  cumplcte 
mechanical  or  other  disintegration  of  the  protoplasm; 
and  (B)  those  which  continue  only  while  the  ])rot()j)lasm 
remains  structurally  intact  and  "living."  The  fomier 
group  (A)  includes  a  large  number  of  hydrolyses  and 
some  oxidations;  e.g.,  those  due  to  oxidases;  hut.  as 
already  indicated,  the  physiologically  significant  oxida- 
tions, especially  of  sugar  and  other  energ^'-yielding 
compounds,  cannot  be  accomplished,  at  least  with 
anything  like  the  noniial  velocity  and  comi)leteness, 
under  the  influence  of  enz>Tnes  or  cell-extracts.  Yeast 
cells  which  have  been  mechanically  destroyed,  or  even 
simple  water}'  extracts  of  yeast,  rapidly  hydrolyze  cane 
sugar,  just  as  does  the  living  cell,  and  autolyzing  yeast 
cells  split  proteins  rapidly  into  amino-acids.  It  has  been 
found,  howxver,  that  the  alcohohc  femientation  of  sugar 
proceeds  much  more  slowly  in  the  press-juice  of  yeast 
than  it  does  under  the  influence  of  the  living  protoplasm.' 
Many  other  cases  are  known  where  biochemical  reactions, 
although  proceeding  in  dead  cells  or  under  the  influence 
of  cell-extracts,  do  so  at  a  slower  rate  than  in  living 
protoplasm. 

The  latter  group  of  reactions  (B)  include  the  spcciuc 
syntheses,  i.e.,  of  protein,  together  with  those  syntheses 
which  require  the  expenditure  of  considerable  energ)-. 
like  the  building  up  of  fats  from  carbohydrate,  or  of 
amino-acids  and  other  compounds  of  high  chemical 
potential  from  compounds  of  lower  i)otential.  The 
energy-  required  for  these  syntheses  is   apparently  de- 

»Cf.  Harden,  "Alcoholic  Fermentation,"  in  Momgraphs  on  Bio- 

chemislry,  edited  by  Plimmcr  and  Hopkins. 


54    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

rived  from,  the  oxidation  of  other  compounds,  especially 
carbohydrates.^ 

It  is  especially  significant  that  in  all  cases  the  synthesis 
of  specific  proteins,  the  reactions  essential  to  growth 
and  maintenance,  requires  the  intact  protoplasmic 
structure.  These  syntheses  constitute  the  chemical 
reactions  most  highly  characteristic  of  the  living  state. 
At  one  time  it  was  believed  that  all  of  the  metabolic 
syntheses  were  the  result  of  the  special  activity  of 
living  protoplasm,  and  that  the  chemical  reactions  of 
dead  protoplasm  or  cell-extracts  were  always  of  a 
catabolic  (splitting)  kind;  it  is  now  known,  however, 
that  various  syntheses  involving  little  change  of  energy, 
e.g.,  the  synthesis  of  esters  and  disaccharides,  readily 
occur  under  the  influence  of  enzymes  alone.  Yet  the 
fundamental  fact  remains  that  the  more  important  or 
specific  part  of  the  synthetic  activity  of  protoplasm  is 
exhibited  only  during  life.  A  relation  of  the  normal 
protoplasmic  structure  to  certain  types  of  chemical 
action,  especially  synthetic  action,  is  thus  indicated. 
With  the  alteration  of  structure  occurring  at  death,  as 
indicated  by  loss  of  semi-permeability,  coagulation  of 
cell-proteins,  and  other  phenomena  of  disintegration,  is 
associated  a  loss  of  synthetic  power.  Only  the  living 
yeast  cell  can  build  up  from  a  solution  of  sugar,  tartrates, 

^  Hence  the  importance  of  carbohydrates  for  growth  and  assimila- 
tion; e.g.,  in  plants,  carbohydrate  is  indispensable  for  the  assimilation 
of  amino-acids  by  yeast  and  molds  (cf.  the  series  of  papers  by  F.  Ehr- 
lich,  Biochem.  Zeitschrift,  I,  VIII,  XVIII,  XXXVI  (1906-11);  similarly 
in  higher  plants  the  synthesis  of  proteins  from  amides  in  germination 
requires  the  presence  of  carbohydrates  (cf.  Jost's  Physiology  of  Plants, 
p.  175,  for  a  summary  of  the  chief  facts).  The  sequence  of  metabolic 
derangements  associated  with  diabetes  shows  the  fundamental  importance 
of  carbohydrate  metabolism  in  higher  animals. 


PROTOPLASM  AS  A  PHYSICAL  SYSTEM  55 

and  inorganic  salts  the  various  special  compounds, 
definite  and  constant  in  number,  proportions,  and 
distribution,  which  compose  the  yeast  protoplasm. 

Some 'of  the  changes  in  the  chemical  reactivity  of 
protoplasm  resulting  from  mechanical  or  other  destruc- 
tion of  the  living  cells  or  tissue  are  well  illustrated  by 
Fletcher's  and  Hopkins'  work  on  the  formation  and 
disappearance  of  lactic  acid  in  muscle;^  also  by  the  work 
of  Harden  and  Maclean  on  oxidation  by  isolated  animal 
tissues;^  and  more  recently  by  Warburg's  detenninations 
of  the  oxygen  consumption  in  living  cells  (sea-urchin 
eggs,  blood  corpuscles,  bacteria,  etc.)  as  compared  with 
that  of  the  same  cells  after  death  or  fme  mechanical 
subdivision.^  In  all  of  these  cases  chemical  activity 
is  greatly  decreased  when  the  protoplasmic  structure  is 
artificially  destroyed.  Warburg  has  also  shown  that 
when  certain  cells,  the  blood  corpuscles  of  birds,  are 
mechanically  broken  down  by  freezing  and  thawing, 
the  oxygen  consumption  exhibited  by  the  residue  is 
associated  with  the  more  solid  part  of  the  complex— that 
which  can  be  separated  by  centrifuging;  similarly,  in 
liver  cells  the  separable  granules  have  a  relatively  high 
oxygen  consumption.^  A  relation  of  oxidative  activity 
to  the  solid  part  of  the  protoi)lasmic  structure  is  thus 
indicated.  In  some  cases  it  can  be  shown  micro- 
chemically  that  certain  oxidations  (the  indophenol 
reaction)  occur  most  actively  at  the  surfaces  of  solid 

»  Fletcher  and  Hopkins,  Journal  of  Physiology,  XXXV  (1907).  ^47- 

2  Harden  and  Maclean,  Journal  of  Physiology,  XLHI  (loi  iV  34- 

3  Warburg,  Ergdmisse  der  Physiol.,  XIV  (iQU),  253- . 

4  Warburg,  cf.  Biochcm.  Zeitschrifl,  CXIX  (1921),  134,  and  references 
to  earlier  papers  there  given. 


56    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

structures,  such  as  the  nuclear  and  plasma  membranes.^ 
It  is  interesting  to  note  that  a  visible  alteration  or 
breakdown  of  protoplasmic  structure  seems  always  to 
be  associated  with  the  death  process,  however- induced; 
even  after  natural  death,  coagulative  or  other  alterations 
occur  in  most  forms  of  protoplasm;  death  rigor,  increased 
permeability,  and  loss  of  tensile  strength  in  muscle  cells, 
are  examples  of  such  effects.  The  death  change  involves 
a  structural  disintegration,  with  which  is  associated  a 
loss  of  normal  chemical  activity. 

A  second  class  of  cases,  in  which  certain  chemical 
reactions  may  be  promoted  instead  of  hindered  by  the 
breakdown  of  normal  cell  structure,  also  throws  light 
upon  the  relation  of  structure  to  the  chemical  activity 
of  protoplasm;  an  example  is  the  autolytic  breakdown  of 
proteins  or  of  glycogen  in  dead  liver  cells  or  other 
autolyzing  cells.  The  rate  of  such  breakdown  is 
increased  when  the  structure  is  altered  by  death,  and 
still  more  so  (according  to  Chiari's  observations)  in 
the  presence  of  lipoid-solvent  compounds  like  chloroform.'' 
Such  facts  illustrate  another  form  of  chemical  control 
exercised  by  protoplasmic  structure.  Apparently  they 
indicate  that  a  partitioned  or  alveolar  structure  exists 
during  life;  enzyme  and  substrate,  for  example,  may  thus 
be  kept  apart  while  this  structure  is  intact,  but  on  death 
the  interalveolar  partitions  are  broken  down  and  inter- 
action results.  It  has  been  suggested  by  Hofmeister^ 
that  this  chambered  tynpe  of  architecture  is  what  renders 
it  possible  for  a  variety  of  chemical  reactions  to  occur 

^  R.  S.  Lillie,  Journal  of  Biological  Chemistry,  XV  (1913),  237. 
^  Chiari,  Arch,  exper.  Path.  Pharmakol.,  LX  (1909),  256. 
3  Hofmeister,  loc.  cit. 


PROTOPLASM  AS  A  PHYSICAL  SYSTEM  57 

within  the  limits  of  a  single  cell  without  mutual  inter- 
ference; different  metabolic  processes  are  thus  localized, 
a  necessary  condition  for  a  definite  ''chemical  organiza- 
tion" of  the  cell. 

It  is  well  known  that  when  living  protoplasm  is 
acted  upon  by  cytolytic  agents  or  heat  (40°)  or  is  altered 
mechanically  or  osmotically  (i.e.,  by  h^-pertonic  or 
h^'potonic  media)  beyond  a  certain  degree,  chemical 
changes  are  induced  in  it  which  are  absent  or  inaj)preci- 
able  under  normal  conditions.  These  changes  are  as- 
sociated with  profound  structural  alteration,  as  shown 
by  coagulation  of  the  cell-proteins,  changes  of  permea- 
bility and  water  content,  and  loss  of  the  noniial  tensile 
and  other  mechanical  properties  of  the  protoplasm. 
Thus  in  muscle,  and  probably  in  most  other  cells,  lactic 
acid  is  formed  in  large  quantity;  in  many  cells  autolytic 
changes  are  initiated;  in  oxidase-containing  fruits  and 
tubers  (apple,  potato)  the  browning  reaction  occurs; 
and  in  many  cases  (muscle)  there  is  a  marked  temporary 
increase  in  the  output  of  CO^.  Of  special  interest  is 
the  fact  that  these  changes  are  associated  with  a  loss 
of  the  nonnal  semi-permeability  of  the  plasma  mem- 
branes, coincidently  with  a  loss  of  the  characteristic 
water-immiscibility  of  the  protoplasm  as  a  whole;  hence 
disintegration  by  diffusion  processes  follows  rapidly. 
These  effects  are  such  as  might  be  expected  to  result 
from  a  breakdown  of  the  normal  partitioned  structure 
of  the  system.  Materials  which  during  life  are  kei)t 
apart  by  the  interposition  of  films  are  thus  enabled  to 
interact;  hence  (as  already  cited)  autolysis  is  accelerated 
by  cytolytic  compounds  like  chlorofomi.  For  a  similar 
reason  the  minuter  structural  elements  -which  nonnally 


58  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

are  prevented  by  the  pervading  film-structure  from  fusing 
or  otherwise  losing  their  identity — undergo  alteration  or 
breakdown;  a  general  coarsening  or  increase  of  opacity, 
indicating  coagulative  changes  in  the  cell  proteins,  is 
characteristic  of  dying  protoplasm,  and  is  associated  with 
the  changes  in  mechanical  properties  described  above.^ 

The  basis  of  these  changes  is  insufficiently  understood 
at  present,  but  their  ready  production  by  lipoid-solvent 
compounds  seems  to  indicate  that  the  lipoid  constituents 
of  the  protoplasm  are  specially  involved.  Apparently 
the  Hpoids  have  a  relation  to  the  protein  constituents 
resembling  that  which  a  '^protective  colloid"  (gelatine) 
added  to  a  suspensoid  hydrosol  (gold)  has  to  the  colloidal 
particles  of  the  suspensoid.  In  the  presence  of  the 
protective  substance  the  particles  remain  separate  under 
conditions,  such  as  the  presence  of  salts  or  increase  of 
H-ion  concentration,  which  otherwise  lead  to  fusion  or 
precipitation;^  this  stabilizing  influence  is  apparently 
dependent  on  the  formation  of  thin  adsorption  films 
about  the  particles.  In  the  case  of  living  protoplasm, 
the  evidence  from  cytolysis  and  similar  phenomena 
indicates  that  the  normal  fine  subdivision  of  the  struc- 
tural proteins — shown  by  the  characteristic  translucency 
during  life — is  dependent  on  the  presence  of  thin  lipoid 
films  (possibly  soap)  at  the  surface  of  the  protein  particles, 
fibrils,  or  other  structural  elements.  When  these  films 
are  broken  down  or  destroyed,  a  coalescence  of  particles 
and  a  coarsening  of  structure  result;  these  effects  involve 
a  loss  of  semi-permeability,  together  with  the  changes 

^  The  progress  of  structural  changes  of  this  kind  can  be  followed  by 
the  microscope  under  dark  ground  illumination;  cf.  Aggazzotti,  Z.  allg. 
Physiol.,  XI  (1910),  249. 

*  Zsigmondy,  Colloids  and  UUramicroscopy. 


PROTOPLASM  AS  A  PHYSIC.VL  SYSTEM  59 

in  mechanical  and  chemical  properties  already  described. 
On  such  a  view  the  cytolytic  action  of  lipoid-alterant 
compounds  may  be  explained.  Such  comi)()un(ls  act 
by  destroying  the  film- structure;  hence,  in  adcHtion  to 
destruction  of  semi-permeability,  they  break  down  the 
intracellular  partitions  and  induce  chemical  reactions  of 
the  above-described  kind  and  cause  coagulation  of  the 
cell-proteins.  In  irritable  cells  such  compounds  have 
also  a  strongly  stimulating  action  of  an  irreversii)le  kind, 
as  shown  in  the  contraction  produced  in  muscle  cells, 
and  similar  effects. 

The  above-described  loss  of  translucency  accompany- 
ing cytolytic  or  mortiferous  processes  is  a  phenomenon  of 
much  interest,  which  has  an  intimate  bearing  on  the 
general  problem  of  protoplasmic  structure.  This  change 
is  shown  with  great  clearness  in  all  of  the  more  transpar- 
ent forms  of  protoplasm;  e.g.,  the  eggs  of  marine  animals 
(starfish,  etc.),  protozoa,  and  muscle  cells.  Some  years 
ago  while  studying  the  conditions  of  activity  in  the  cteno- 
phore  swimming  plate — a  beautiful  example  of  a  clear 
translucent  protoplasm,  consisting  of  parallel  contractile 
fibrils  (fused  ciha) — I  was  struck  with  the  constancy  and 
definiteness  of  the  relations  existing  between  changes  of 
translucency  and  changes  of  contractile  activity.  In 
dying  animals  the  plates  become  partially  clouded  and 
adopt  a  rapid  unintermittent  movement,  ditTering  from 
the  normal  movement  in  being  of  quicker  rhythm  and  in 
no  longer  showing  the  mechanical  inhibition  described 
above;  this  movement  continues  until  linally  the  plate 
becomes   white   and   opaque   and   all   activity   ceases.* 

'R,  S.  Lillie,  American  Journal  of  Physiology,  X\'I  (1906),  117; 
XXI  (1908),  200. 


6o  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

A  similar  cycle  of  alteration  is  passed  through,  only 
more  rapidly,  when  the  normal  plates  are  transferred 
from  sea  water  to  various  unbalanced  solutions,  such  as 
pure  isotonic  NaCl;  the  plates  then  exhibit  for  a  brief 
period  (one  or  two  minutes)  an  extremely  active  vibratory 
movement,  which  is  associated  with  a  progressive 
whitening  or  coagulation.  In  general  the  rate  of  coagula- 
tion is  more  rapid  the  more  energetic  the  contractile 
activity;  and  it  is  especially  noteworthy  that  the  coagula- 
tive  process  does  not  begin  until  the  plate  starts  vibrat- 
ing; the  vibration  then  continues  until  the  whole  struc- 
ture is  opaque.  This  change  of  structure  is  irreversible, 
and  at  the  end  the  plate  is  so  altered  in  consistency  that 
it  readily  falls  to  pieces  when  shaken.  Evidently  the 
contractile  activity  is  associated  with  the  removal  of  some 
substance  or  condition  which  prevents  the  coalescence  of 
the  protein  particles  forming  the  fibrils.  A  film-structure 
of  the  kind  suggested  above  seems  indicated,  which  is 
broken  down  by  the  action  of  the  solution  with  the 
production  of  both  chemical  and  mechanical  effects. 
The  general  relations  between  such  effects  and  stimula- 
tion processes  will  be  considered  in  more  detail  below. 
Apparently  in  the  swimming  plate  the  essential  effect 
produced  by  the  unbalanced  solution  is  an  acceleration 
or  intensification  of  the  normal  processes  of  stimulation 
and  contraction;  a  dependence  of  these  processes  on 
the  alteration  or  removal  of  film  material  is  thus  indicated. 
The  indications  are  that  during  the  normal  rhythm  of 
contraction  in  sea  water  the  film-structure  is  alternately 
broken  down  and  reformed  in  each  contractile  cycle. 
Presumably  under  the  abnormal  conditions  resulting 
from  the  action  of  the  pure  NaCl  solution  the  rate  of 


PROTOPLASM  AS  A  PHYSICAL  SYSTEM  6i 

breakdown  is  increased,  and  the  restoration  of  lilm- 
structure  between  successive  contractions  becomes  im- 
perfect, with  the  result  that  eventually  the  whole  struc- 
ture disintegrates.  These  effects  may  be  compared  with 
those  of  excessive  fatigue,  which  also  leads  to  irreparable 
structural  breakdown.^ 

STRUCTURE  OF  PROTOPLASM 

It  will  be  evident  from  the  preceding  discussion  that 
structure  is  only  one  factor  in  the  chemical  activity  of 
protoplasm;  undoubtedly  many  other  factors— those 
entering  in  all  chemical  reactions,  such  as  concentration, 
temperature,  special  affinities,  catalysis — enter  in  deter- 
mining the  rate  and  character  of  the  metabolic  reactions. 
But  the  controlling  factor— that  which  is  subject  to 
rapid  and  reversible  alteration  under  the  intluence  of 
stimulating  agencies — appears  to  be  the  peculiar  structure 
of  the  living  substance.  By  the  conception  of  ''struc- 
ture" as  applied  to  protoplasm  is  meant,  generally 
speaking,  the  distribution  of  the  physically  stabler 
components,  usually  the  solid  components,  of  the  system. 
Evidently,  as  already  pointed  out,  this  structure  is 
itself  a  product  of  metabolism;  but  having  once  been 
formed,  it  influences  the  further  course  of  metabolism— in 
the  general  manner  of  which  Child's  comparison  of  the 
living  organism  to  the  flowing  river''  gives  a  good  illustra- 
tion by  analogy.  In  the  living  organism  there  is  always 
structure  of  a  definite  kind;  even  the  simplest  "undilTcr- 

^  Cf.  the  instances  of  structural  alterations  in  the  central  nervous 
system  described  in  Crile's  recent  book,  ,1  Physical  Interpretation  of 
Shock y  Exhaustion,  and  Restoration,  London  (1921). 

^  Cf.  Child,  The  Regulatory  Process  in  Organisms,  Journal  of  Mor- 
phology, XXII  (1911),  171;  also  Senescence  and  Rejuvenescence,  chap.  i. 


62  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

entiated"  protoplasm  is  not  homogeneous,  and  it  is 
necessary  to  reach  a  clear  conception  of  the  essential 
nature  of  this  structure  in  the  most  generalized  forms 
of  living  substance  if  we  are  to  be  in  a  position  to  under- 
stand the  fundamental  conditions  of  physiological  activity. 

That  metabolism  is  controlled  by  structure  is  seen 
in  many  well-known  physiological  facts  already  referred 
to  in  part;  e.g.,  the  course  of  development,  with  the 
associated  constructive  metabolism,  may  in  many  eggs 
or  embryos  be  profoundly  modified  by  artificially 
altering  the  structure  of  the  system.  Developmental 
processes  are  frequently  initiated  by  mechanical  means; 
cases  of  regeneration  illustrate  this,  or  cases  where 
injury  of  the  egg-surface  (pricking  in  the  case  of  the 
frog's  egg,^  or  any  kind  of  cytolytic  action  in  echinoderm 
eggs)''  initiates  cleavage  and  development.  Mechanical 
treatment  causes  stimulation  in  innumerable  instances; 
in  others  it  causes  inhibition.  In  all  of  these  cases  the 
energy  for  the  developmental  or  other  response  comes 
directly  or  indirectly  from  metabolic  processes.  This 
sensitivity  to  the  action  of  mechanical  agents,  which  by 
their  impact,  pressure,  or  other  effects  locally  modify 
cell  structure,  is  perhaps  the  clearest  proof  of  the  intimate 
relations  existing  between  structure  and  function  in 
living  protoplasm. 

In  physical  chemistry  the  importance  of  structural 
conditions  as  modifying  factors  in  chemical  reactions  is 
illustrated  in  the  so-called  heterogeneous  catalyses. 
In    these   phenomena    the   acceleration   of   reaction   is 

*  Guyer,  Science,  XXV  (1907),  910;  Bataillon,  Arch.  zool.  exper. 
et  generate,  XL VI  (1910),  103. 

2  Loeb,  Artificial  Parthenogenesis  and  Fertilization,  University  of 
Chicago  Press  (19 13). 


PROTOPLASM  AS  A  PHYSICVL  SYSTEM  63 

dependent  chiefly  on  surface  effects,  of  which  two  classes 
appear  to  be  especially  important  from  the  biolo;]jical 
point  of  view:  (i)  adsorption  effects,  leading  to  increased 
concentration  at  surfaces  and  hence  increased  reaction- 
velocity;  and  (2)  electrolytic  effects,  due  to  the  existence 
of  local  potential  differences  between  different  regions  of 
the  surface  separating  the  two  phases;  when  both  phases 
conduct  electricity,  local  circuits  may  thus  arise,  furnish- 
ing the  conditions  for  electrolysis.  This  latter  effect  may 
also  be  regarded  as  a  form  of  catalysis,  and  is  illustrated 
in  the  spreading  of  rust  spots  on  iron  surfaces,  or  the 
periodic  catalysis  of  H2O2  by  mercury.  Both  kinds  of 
effects  are  of  fundamental  importance  in  protoi)lasmic 
processes,  as  will  be  show^n  in  more  detail  later.  Other 
conditions  characteristic  of  surfaces  may  also  enter 
(see  pp.  217  ff.). 

As  already  pointed  out,  all  forms  of  protoplasm 
exhibit  the  power  of  specific  synthesis  characteristic  of 
life.  The  constructive  metabolism  by  which  the  specific 
structural  elements  are  built  up  and  maintained  must, 
like  other  forms  of  metabolism,  be  under  the  control  of 
structure.  This  synthetic  activity,  being  a  universal 
property  of  living  matter,  is  undoubtedly  to  be  correlated 
with  the  most  general  or  fundamental  t}'])e  of  structure 
exhibited  by  protoplasm.  In  correspondence  with  its 
uniformity  of  essential  chemical  composition  and  chemical 
behavior,  protoplasm  must  also  possess  a  uniformity  in 
its  essential  type  of  physical  structure;  underhing  the 
variety  of  structural  detail  must  be  some  characteristic 
type  of  structural  composition  common  to  all  forms  of 
protoplasm,  and  determining  the  special  features  of  its 
chemical    activity.     The    traditional    problem    of    the 


64    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

structure  of  protoplasm  is  thus  intimately  bound  up 
with  the  basic  problem  of  general  physiology. 

The  problem  relates  to  the  nature  of  the  structure 
in  living  protoplasm.  All  observers  agree  that  cell 
structure  is  profoundly  altered  by  death;  disintegration 
then  follows,  accompanied  by  diffusion  of  the  cell 
constituents  into  the  surrounding  medium.  As  already 
described,  the  death  of  the  cell  is  associated  with  loss  of 
its  normal  osmotic  properties  or  semi-permeability;  the 
normal  electrical  polarization  also  disappears  at  the  same 
time;  both  phenomena  are  characteristic,  and  indicate 
interruption  in  the  continuity  of  the  protoplasmic 
boundary  layer.  The  most  obvious  general  structural 
changes  occurring  in  the  cell  interior  at  death  are  of  a 
coagulativekind;  the  protoplasm  loses  its  normal  trans- 
lucency  and  becomes  more  opaque  (death  rigor  or  death 
coagulation).  This  effect  is  seen  in  the  greatest  variety 
of  cells  and  organisms,  especially  those  with  translucent 
protoplasm,  as  cited  above.  The  protoplasm  of  muscle 
cells  becomes  more  opaque  and  loses  its  coherency  or 
tensile  strength;  dying  swimming  plates  whiten  and  fall 
to  pieces  on  shaking,  and  other  phenomena  of  a  similar 
kind  are  well  known  to  all  biologists.  Many  observations 
on  the  postmortem  alterations  of  structure  have  been  made 
since  the  introduction  of  the  methods  of  microdissection. 
Kite  and  Chambers  describe  dying  cells  as  losing  their 
viscidity  and  as  being  easily  torn  to  pieces.  Chambers 
describes  the  isolated  nerve-ganglion  cells  of  the  lobster 
as  undergoing  irreversible  structural  changes  when 
mechanically  injured;  the  protoplasm  then  ^'sets  into  a 
coagulated  non-viscous  mass  which  may  be  broken  into 
non-glutinous  pieces."     Taylor  describes  a  similar  break- 


PROTOPLASM  AS  A  PHYSICAL  SYSTEM  65 

down  of  protoplasmic  structures  in  Protozoa  after  injury 
with  the  microdissection  needle.^ 

Facts  of  this  kind  show  again  that  the  maintenance 
of  a  certain  characteristic  type  of  structure  is  an  essential 
part  of  normal  protoplasmic  activity.  The  structure  of 
living  protoplasm  is  not  to  be  conceived  as  resultiiv^ 
from  a  combination  of  static  parts  like  the  structure  of  a 
machine;  it  is  the  product  or  expression  of  continual 
synthetic  activity  and  persists  only  while  metabolism 
persists;  it  expresses  the  constructive  activity  of  metab- 
olism, very  much  in  the  same  manner  as  the  structure 
of  a  flame  or  of  a  fountain  expresses  the  dynamic  activity 
of  such  a  system.  If  the  activity  disappears,  so  also 
does  the  characteristic  structure  or  configuration  which 
is  maintained  by  that  activity.  In  this  sense,  structure 
in  living  protoplasm  is  to  be  conceived  as  continualh* 
in  process  of  formation;  i.e.,  as  an  index  of  the  underlying 
synthetic  reactions  which,  as  already  seen,  are  inseparable 
from  the  chemical  activity  of  the  system  during  life. 
The  apparently  static  condition  represents  in  reality  a 
state  of  balance  betw^een  construction  and  disintegration. 

Yet  a  certain  permanent  or  stable  structural  consti- 
tution (at  least  relatively  permanent)  has  to  be  assumed, 
just  as  in  the  case  of  the  fountain  or  candle  flame.  This 
is  necessary  if  the  dependent  processes  of  chemical  trans- 
formation are  to  exhibit  constant  characters.  The 
physical  nature  of  this  permanent  or  persistent  structural 
substratum  of  living  protoplasm  has  first  to  be  considered. 

^  Kite  and  Chambers, 5«e;;cg, XXXVI  (191 2),  640.  Chambers,  Trans. 
Royal  Soc.  Can.,  XII  (1918),  Series  3,  43;  Taylor,  Uuivrrsity  of  California 
Publications,  XIX  (1920),  403,  cf.  pp.  420,  424,  434.  Mention  has  already 
been  made  of  Aggazzotti's  observations  with  dark  ground  illumination  on 
the  structural  changes  produced  in  blood  corpuscles  by  cytolytic  agents. 
Cf.  also  Traube  and  Klein,  Biochem.  Zeits.,  CXXX  (1922),  477. 


CHAPTER  V 

PHYSICAL  NATURE  OF   PROTOPLASMIC  STRUCTURE: 
IMPORTANCE  OF  SURFACE  CONDITIONS 

It  is  not  possible  here  to  review  in  detail  the  numerous 
and  frequently  conflicting  conceptions  of  protoplasmic 
structure.  The  details  made  visible  by  microscopical 
technique  are  of  so  varied  a  kind  that  none  of  the  many 
attempts  at  unification  have  met  with  universal  agree- 
ment. A  chief  difiiculty  has  been  that  most  histological 
investigators  seem  to  have  conceived  of  protoplasmic 
structure  as  existing  independently  of  the  chemical  and 
physiological  activities  of  the  living  system,  and  not  as 
both  dependent  upon  and  determining  these  activities. 
Some  conception  of  structure  is  required  which  will  be 
general  enough  to  apply  to  all  of  the  forms  of  living 
matter,  and  which  will  at  the  same  time  enable  us  to 
understand  the  dependence  of  the  fundamental  vital 
properties  of  specific  synthesis  and  irritability  upon 
structure.  It  may  be  doubted  whether  we  are  yet  in  a 
position  to  form  a  clear  and  permanently  vaKd  concep- 
tion of  protoplasmic  structure,  but  with  the  progress  in 
our  knowledge  of  the  properties  of  colloidal  systems  has 
come  what  appears  to  be  an  increased  insight  into  the 
possibilities.  The  problem  may  be  defined  in  its  essential 
terms,  as  follows:  Can  a  system,  with  components  of  the 
kind  which  we  find  present  in  all  living  matter,  be  ima- 
gined which  will  exhibit,  as  a  correlative  of  its  structural 
composition,  the  above-described  properties  of  specific 
growth,    sensitivity    to    electrical   conditions,    catalytic 

66 


PROTOrLASjMIC  STRUCTURE  67 

activity,  and  automatic  regulation  of  composition  and 
properties  ? 

The  experimental  studies  and  observations  of  the  last 
twenty  years  have  led  more  and  more  to  the  conclusion 
that  the  general  or  fundamental  structure  of  pn)lo])lasm 
corresponds  more  closely  to  that  of  an  emulsion  than  to 
that  of  any  other  simple  non-Uving  physical  system. 
The  most  general  facts  of  its  chemical  composition  are  in 
agreement  with  this  conclusion.  Water-insoluble  con- 
stituents (lipoids)  occur  in  association  with  colloidal 
constituents  which  have  water-combining  powers  (pro- 
teins). The  whole  resulting  complex  is  during  life 
immiscible  with  water,  and  typically  is  bounded  from 
the  external  watery  medium  forming  its  immediate 
environment  by  a  layer  or  surface-film  having  semi- 
permeable properties.  The  semi-permeability  and  the 
water-immiscibility  of  the  surface  layer  appear  to  be 
interdependent  properties;  they  suggest  the  existence  of 
a  continuous  external  layer  of  water-insoluble  material 
of  fatty  or  similar  nature.^  The  unit'  of  organic  struc- 
ture, the  cell,  would  thus  appear  to  be  a  system  with 
an  aqueous  internal  phase  limited  externally  b}'  a  thin 
water-insoluble  phase  or  boundary  layer.  The  aqueous 
internal  phase  forms  one  component  of  a  system,  the 
cell  protoplasm,  which  is  structural! \'  and  chemically 
highly  complex,  and  emulsion-like  in  its  general  physical 
constitution. 

It  is  evident  that  the  general  properties  of  emulsions 
do  not  in  themselves  explain  the  properties  of  living 
matter.  What  seems  highly  probable,  however,  is  that 
the  original  structural  foundation  upon  which  the  proper- 

'  Cf.  Quincke,  Ann.  Physik.,  XXXV  (1888),  580;   cf.  pages  629-30. 


68    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

ties  of  living  matter  have  arisen — or  which  has  made  it 
possible  for  systems  with  vital  properties  to  evolve — 
is  that  of  an  emulsion;  i.e.,  a  pol>^hasic  system  with  thin 
interfacial  films  separating  two  or  more  component 
phases  which  have  fluid  or  solvent  properties.  From 
general  considerations  it  seems  clear  that  some  kind  of 
polyphasic  structure  must  be  assumed  in  order  to  account 
for  such  a  universal  property  as  that  of  growth;  the  unit 
of  living  matter,  even  while  it  continues  to  increase  in 
size,  retains  a  complex  and  specific  composition  different 
from  that  of  the  surroundings;  and  this  peculiarity  is  in 
itself  incompatible  with  structural  homogeneity,  since 
the  elementary  need  of  providing  against  free  diffusive 
interchange  with  the  surroundings  requires  a  surface 
layer  with  properties  different  from  those  of  the  internal 
protoplasm.  This  must  be  true  even  of  the  simplest 
forms  of  living  matter.  We  cannot  compare  the  proto- 
plasm of  ultra-microscopic  organisms  with  self-propa- 
gating enz>Tne-like  material  (supposing  such  material 
possible),  as  has  been  done,  since  the  physical  con- 
ditions necessary  for  metabolism  and  growth  must 
exist  in  even  the  simplest  living  systems;  and  this 
requires  at  the  very  least  a  differentiation  between  the 
more  permanent  or  solid  components  of  the  system  and 
the  liquid  components  w^hich  contain  in  solution  simpler 
materials  (nutrients  and  oxygen)  which  are  continually 
being  renewed. 

It  has  long  been  recognized  that  colloids  form  the 
basis  of  protoplasmic  structure.  Hardy's  investigations 
showed  that  many  of  the  characteristic  structural 
appearances  presented  by  fixed  and  stained  protoplasm 
in  microscopic  preparations  were  incidental  consequences 


rROTOPLASJMIC  STRUCTURE  69 

of  the  colloidal  composition  of  the  system  and  not  expres- 
sions of  any  distinctively  vital  condition  or  structure. 
He  and  others  have  demonstrated  that  similar  appear- 
ances can  be  produced  by  fixation  in  a])parenllv  homo- 
geneous colloidal  solutions  or  gels  (egg-white,  gelatine).* 
Hardy  also  pointed  out  various  parallels  between  the 
processes  of  gelation  in  artificial  colloidal  systems  and  the 
changes  of  physical  state  in  living  protoplasm.'  From 
these  and  related  facts  it  became  clear  that  if  we  are  to 
draw  conclusions  regarding  protoplasmic  structure  from 
the  appearances  seen  in  microscopic  preparations,  the 
general  nature  of  the  changes  produced  in  colloidal 
systems  by  physical  and  chemical  agents  must  first  be 
determined.  Great  impetus  w^as  thus  given  to  the 
study  of  the  physics  and  chemistry  of  colloids,  a  subject 
then  in  its  early  stages,  and  also  to  the  study  of  the 
structure  and  physical  properties  of  protoplasm  in  the 
living  condition. 

Various  resemblances  between  living  protoplasm  and 
emulsions  were  long  ago  described  by  Biitschli.-'  These 
resemblances  relate  both  to  structure  and  to  certain 
peculiarities  of  behavior;  e.g.,  amoeboid  movement 
and  modifications  of  activity  b>'  changes  in  the  sur- 
roundings. Biitschli  reached  the  conception  that  a 
''foam  structure,"  corresponding  essentially  to  a  film- 
pervaded  or  chambered  structure,  is  the  t>'])e  most 
generally  exhibited  by  living  protoplasm.-* 

» W.  B.  Hardy,  Journal  of  Physiology,  XXXV  (1899),  158;  cf.  also 
Alfred  Fischer, Fixierung,Farbung,u)id  Ban  des  Prolo plasmas, ]cnA  (1899). 

2  Hardy,  Proceedings  of  the  Royal  Society,  LX\'I  (1S99),  1 10. 

3  Biitschli,  Microscopic  Foams  and  Protoplasm. 

4Cf.  the  discussion  by  E.  B.  Wilson,  Jour.  Morph.,  X\  (1899), 
Supplement. 


70  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

The  subject  of  the  physical  chemistry  of  emulsions 
forms  a  part  of  the  now  extensively  developed  field  of 
colloid  chemistry,  and  cannot  be  considered  here  in 
any  detail.  Some  of  the  more  general  facts  relating  to 
the  structure  and  properties  of  emulsions  must,  however, 
be  discussed  briefly,  since  a  clear  conception  of  the  physi- 
cal conditions  existing  in  these  systems  is  necessary 
before  proceeding  to  the  consideration  of  the  more 
complex  types  of  structure  and  behavior  which  have 
evolved  in  living  matter,  apparently  with  emulsion- 
systems  of  a  relatively  simple  kind  as  a  basis. 

EMULSIONS^ 

Emulsions  and  foam  structures  are  essentially  similar 
systems,  with  the  difference  (as  usually  defined)  that  in  a 
foam  the  disperse  or  discontinuous  phase  is  a  gas,  in  an 
emulsion  a  liquid.  Jellies  or  gels  also  resemble  these 
systems  in  constitution  in  many  cases.  It  is  now  known 
that  various  different  types  of  gel  structure  exist; 
many  jellies,  however,  are  essentially  dense  emulsions; 
thus  stiff  foams  of  air  with  a  soap  solution  (or  solutions 
of  albumin,  saponin,  or  other  surface-active  colloidal 
substances)  have  many  of  the  characters  of  solids  or 
semi-solids;  i.e.,  permanence  of  form,  elasticity,  high 
viscosity;  and  all  transitions  between  liquid  and  solid 
systems  of  the  emulsion  type  are  known — a  fact  familiar 
to  anyone  who  makes  a  lather  of  soap  solution.  The 
same  is  true  of  an  emulsion  of  one  liquid  in  another; 
thus  an  emulsion  of  oil  in  a  soap  solution  may  be  made 

*  For  a  general  review  cf.  Bancroft's  series  of  articles  on  "The 
Theory  of  Emulsification "  in  Journal  of  Physical  Chemistry,  XVI-XIX 
(191 2-15);  also  the  recent  book  of  Clayton,  The  Theory  of  Emulsions 
and  Emulsification. 


rROTOrLASJVIIC  STRUCTURE 


71 


SO  concentrated — with  more  than  90  per  cent  of  oil  as  a 
disperse  phase  in  some  of  the  emulsions  prepared  by 
Pickering' — that  the  whole  mass  has  a  jelly-like  con- 
sistency. The  differences  of  opinion  as  to  whether 
living  protoplasm  belongs  to  the  ''sol"  or  "gel"  t>'])e 
are  thus  seen  to  be  unimportant,  since  transitions  between 
these  states  are  continuous,  and  in  fact  many  forms  of  pro- 
toplasm exhibit  a  liquid  consistency  at  one  stage  (or  under 
certain  conditions)  and  a  solid  consistency  at  another.^ 

In  a  foam  of  air  and  soap  solution  the  individual 
bubbles  do  not  coalesce,  although  the  intervening  lilms 
may  be  extremely  thin;  evidently  the  structural  stability 
of  the  system  as  a  whole  is  determined  by  the  properties 
of  the  films.  If  we  break  down  these  films,  mechanically 
or  otherwise,  the  whole  foam  structure  collapses.  The 
stability  of  emulsions  of  oil  in  aqueous  media  is  similarly 
conditioned;  in  this  case  the  coalescence  of  the  separate 
oil  droplets  is  prevented  by  interfacial  films  of  soap  or 
other  material,  and  such  an  emulsion  can  be  also  de- 
stroyed (de-emulsified)  by  altering  the  material  compos- 
ing the  films,  e.g.,  by  adding  strong  acid  if  soap  is  tlie 
emulsifying  material.  Such  facts  lead  to  the  general 
question  of  the  conditions  detemiining  the  stability  of  a 
foam  structure  or  emulsion. 

Two  chief  conditions  for  the  persistence  of  an  air 
foam  are  that  the  layer  of  solution  separating  the 
adjacent  bubbles  should  have  (i)  a  low  surface-tension 
and  (2)  a  high  viscosity.  A  low  surface-tension  is 
favorable  because  the  tangentially  acting  forces  tending 

1  Pickering,  Journal  of  the  Chemical  Society,  XCI  (1907)1  2001. 
»  Cf.  Bayliss'  recent  paper  in  Proceedings  of  the  Royal  Society,  B, 
XCI  (1920),  196. 


72    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

to  rupture  the  films  or  lamellae  are  then  small;  i.e., 
the  natural  tendency  of  the  film  material  to  minimize 
its  surface,  or  ^'draw  together,"  is  slight.  But  this 
condition  is  not  alone  sufficient,  as  seen  in  the  fact  that 
pure  liquids  of  low  surface-tension  against  air,  like  ether, 
benzol,  alcohol,  etc.,  do  not  give  permanent  foams, 
any  more  than  does  water.  It  is  well  known  that 
mixtures  of  alcohol  and  water  foam  more  readily  than 
either  liquid  alone ;  and  this  is  especially  true  of  mixtures 
of  water  and  a  second  liquid  of  great  surface-activity 
and  high  viscosity,  such  as  amyl  alcohol;  hence  the 
important  generalization  that  pure  liquids  do  not  foam — 
do  not  form  permanent  disperse  systems  with  air.  Nor 
do  mixtures  of  two  pure,  mutually  immiscible  liquids 
readily  form  permanent  emulsions.  Typically  the  pres- 
ence of  a  third  substance  is  necessary,  and  it  is  important 
that  this  third  substance  should  be  of  such  a  kind  as  to 
lower  the  surface-tension  at  the  boundary  between  the 
phases,  and  also  to  impart  to  the  surface  layer  a  relatively 
high  viscosity  or  resistance  to  displacement.  Under  some 
conditions  this  viscosity  may  be  sufficient  to  impart  to 
the  interfacial  layer  the  properties  of  a  solid  film.  In 
general,  a  third  substance  is  effective  as  an  emulsifying 
agent  in  proportion  to  its  power  of  forming  at  the 
boundary  a  film  having  these  properties  of  low  surface- 
tension  and  high  viscosity.  Most  substances  which 
form  stable  emulsions  of  oil  in  water  (soap,  proteins, 
gums)  are  of  this  kind.  The  interfacial  films  or  lamellae 
then  resist  disruption  and  the  disperse  droplets  are 
prevented  from  fusing.  If  the  film  is  considered  as  a 
phase,  most  emulsions  would  be  classed  as  three-phase 
systems  (triphasic). 


PROTOPLASMIC  STRUCTURE  73 

Another  condition  favoring  stability  in  an  emulsion 
is  a  small  diameter  in  the  disperse  droplets.  Thr 
disperse  particles  in  suspensions  and  emulsions  are 
electrically  charged,  and  if  they  are  sufliciently  minute 
the  forces  due  to  their  mutual  electrostatic  repulsion 
may  be  sufficient  to  prevent  contact  and  fusion.*  We 
must  therefore  qualify  the  statement  that  at  least  three 
components  are  necessary  in  a  permanent  emulsion- 
system  by  the  proviso  that  the  subdivision  be  not 
excessively  minute.  This  factor,  however,  is  of  minor 
importance  in  most  emulsion  systems,  and  probably  is 
not  of  great  importance  from  a  biological  point  of  view. 
It  is  worthy  of  note,  however,  that  in  some  cases  mutual 
electrostatic  repulsion  appears  to  play  a  part  in  deter- 
mining the  distribution  of  colloidal  particles,  droplets, 
or  other  minute  freely  mobile  particles  in  cells;  e.g.. 
the  distribution  of  the  chromatin  in  the  equatorial 
plates  and  spiremes  of  mitotic  figures  shows  evidence  of 
this  factor.^ 

An  emulsion,  being  a  system  of  disperse  charged 
particles,  resembles  in  this  respect  any  colloidal  sus- 
pension; hence  electrolytes  influence  the  stability  of 
emulsions,  because  of  the  influence  of  the  ions  on  the 
interfacial  potentials,  just  as  they  influence  the  stability 
of  other  colloidal  systems.^  Generally  speaking,  any 
mechanical,  chemical,  or  electrical  conditions  which 
alter  the  surface  lamella;  affect  the  stabilit\'  and  other 

^  Cf.  Lewis,  Kolloid-Z.,  V  (1909),  91. 

^  R.  S.  Lillie,  American  Journal  of  Physiology,  XV  (1906),  46. 

3  For  the  action  of  electrolytes  on  the  stability  of  emulsions  if. 
Powis,  Z.  physik.  Chan.,  LXXXIX  (1914-15).  i^^'-  ^^-  >^ox\.\no\^ 
and  DeKruif,  /.  Gen.  Physiol.,  IV  (1921-22),  639.  for  an  account  of 
the  analogous  action  of  electrolytes  in  the  agglutination  of  bacteria. 


74    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

properties  of  an  emulsion  system.  Emulsions  of  oil  in 
alkaline  water  or  soap  solution  are  destroyed  by  adding 
strong  acid  (HCl)  which  breaks  down  the  soap  films. 
Similarly  a  foam  structure  may  be  destroyed  mechani- 
cally or  by  adding  a  surface-active  substance  of  low  vis- 
cosity; thus  a  few  drops  of  ether  destroy  a  beer-foam, 
a  fact  explained  by  Quincke  as  due  to  the  displacement 
of  the  material  composing  the  surface  lamellae/  Similarly 
a  saponin  solution  to  which  sufficient  alcohol  is  added 
does  not  form  a  permanent  foam;  the  addition  of  iso- 
butyric  acid  to  a  saponin  solution  also  prevents  foaming, 
but  if  alkali  is  added  to  neutralize  the  acid  and  form  the 
surface-inactive  salt,  foaming  results.^  Many  other 
facts  of  a  similar  kind  are  well  known.  The  conditions 
of  de-emulsification  (''cracking"  of  emulsions)  deserve 
careful  study  by  biologists,  for  changes  of  this  kind  are 
almost  certainly  concerned  in  many  forms  of  protoplasmic 
activity;  e.g.,  secretion  and  the  processes  of  activation, 
stimulation,  and  cytolysis. 

In  general,  therefore,  we  may  define  the  chief  condi- 
tion of  stability  in  emulsion  systems  as  the  presence  of 
material,  differing  from  that  composing  the  two  chief 
phases,  in  the  form  of  thin  continuous  layers  or  films 
deposited  or  adsorbed  at  the  boundary  surfaces.  The 
thickness  of  these  films  may  be  extremely  slight;  when 
a  material  is  surface-active  and  is  free  to  spread  over 
the  surface  separating  the  phases,  conditions  of  equi- 
librium may  not  be  reached  until  the  layer  is  only  one 
or    two   molecules    thick. ^     Such    a   film,    however,    is 

'  Quincke,  Ann.  Physik,  XXXV  (1888),  580. 

2  Zawidski,  Z.  physik.  Chem.,  XXXV  (1900),  77. 

3  Cf.  Langmuir,  Journal  of  the  American  Chemical  Society,  XXXIX 
(1917),  1848;  cf.  also  Freundlich's  Kapillarchemie,  p.  278. 


PROTOPLASMIC  STRUCTURE  75 

capable  of  holding  one  liquid  finely  dispersed  in  another 
in  a  permanent  state  of  emulsion.  We  may  infer  that  in 
at  least  some  forms  of  protoplasmic  emulsion-structure 
the  interfacial  films  are  of  molecular  thickness,  a  con- 
sideration of  much  importance  in  relation  to  the  proper- 
ties of  irritabiUty  and  transmissivity  (or  propagation  of 
excitation-states),  as  will  be  seen  below. 

ADSORPTION 

It  will  be  clear  from  the  above  that  in  the  formation 
of  emulsions — and  hence  of  living  protoplasm  as  a  system 
based  upon  the  emulsion  type  of  structure — the  con- 
ditions determining  the  formation  of  interfacial  films 
are  of  primary  importance.  Adsorption,  the  process 
by  w^hich  material  collects  or  concentrates  at  boundary- 
surfaces,  is  thus  a  fundamental  factor  in  the  fonnation 
and  behavior  of  emulsion  systems  and  of  colloidal  sys- 
tems in  general.  The  physics  and  chemistry  of  adsorp- 
tion processes  have  recently  been  discussed  fully  in 
several  excellent  textbooks,'  so  that  it  is  unnecessar}-  here 
to  give  any  detailed  account.  One  general  fact,  however, 
which  may  be  emphasized  as  especially  important  from 
the  physiological  point  of  view,  is  that  adsorbed  sub- 
stances are  typically  more  subject  to  chemical  change 
than  substances  uniformly  distributed  in  a  solution. 
Both  the  increase  of  concentration  and  the  presence  of 
surface  factors  are  concerned  in  the  increase  of  reactivity, 
the  catalytic  action  of  many  finely  divided  materials 
(charcoal,  platinum,  etc.)  is  usually  referred  to  the 
increased  concentration  of  the  chemically  altered  material 

^Hober,  Physikalische  Chcmic  der  Zclle  und  dcr  Grucbe  (iom); 
Freundlich,  Kapillarchcmie,  Leipzig  (1909);  Bayliss,  Principks  of  Gen- 
eral Physiology;  Bancroft,  Applied  Colloid  Chemistry. 


76  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

at  the  surface  of  the  catalytic  agent,  but  it  appears 
probable  that  other  factors  (electrical)  also  enter  in 
many  cases  of  adsorption-catalysis  (see  below). 

In  considering  the  case  of  protoplasmic  systems,  we 
may  regard  adsorption  as  of  importance  in  two  chief 
respects:  (i)  as  an  essential  condition  in  the  determina- 
tion of  structure  (through  the  formation  of  the 
adsorption-films  of  the  protoplasmic  emulsion  and  in 
membrane  structure  in  general),  and  (2)  as  a  main 
factor  determining  the  character  and  velocity  of  the 
chemical  reactions;  i.e.,  as  influencing  or  controlling 
cell-metabolism. 

It  is  well  known  that  the  adsorption  of  dissolved 
substances  of  low  molecular  weight  is,  as  a  rule,  a  strictly 
reversible  process,  with  the  equilibrium  conditions 
defined  by  the  formula  xjm  =  kcn ,  where  x  is  the  quantity 
adsorbed,  m  the  mass  of  the  adsorbent,  c  the  concentra- 
tion of  the  substances  in  solution,  and  k  and  n  constants. 
On  the  other  hand,  in  the  case  of  colloidal  substances  or 
other  substances  of  high  molecular  weight,  adsorption 
frequently  leads  to  a  change  of  properties,  the  substances 
becoming  converted  into  relatively  insoluble  or  resistant 
varieties'  (possibly  polyanerized) .  In  such  cases  the 
process  may  be  difficultly  reversible  or  irreversible,  a 
fact  of  much  interest  as  bearing  on  the  question  of  the 
conditions  under  which  the  more  permanent  portion 
of  the  protoplasmic  substratum  is  formed.  In  general, 
organic  growth  appears  to  depend  on  the  deposition  of 
relatively  stable  or  persistent  structural  elements  or 
material  in  apposition  to  other  elements  or  material  of 

^  Cf.  Hober,  op.  cit.,  p.  220,  for  instances  of  anomalous  or  irre- 
versible adsorption. 


PROTOrLASiMIC  STRUCTURE 


77 


the  same  kind,  a  process  suggesting  an  irreversiijic 
t>pe  of  adsorption.  A  few  examples  of  irrcversihlc 
adsorption  may  be  cited  for  illustration.  I-'rcundlich 
and  Losev'  found  that  a  solution  of  the  dye,  cr}-stal 
violet,  was  completely  decolorized  by  animal  charcoal, 
and  that  washing  would  not  give  back  the  dye.  This 
may  mean  that  the  concentration  of  the  dye  in  solution 
at  equilibrium  is  indefmitely  small;  but  more  probably 
it  points  to  the  formation  of  an  insoluble  modification 
as  the  result  of  adsorption.  Proteins  like  egg-albumin 
when  adsorbed  at  the  surface  of  drops  of  chloroform, 
form  thin  highly  insoluble  and  resistant  pellicles;  i.e., 
the  protein  undergoes  the  change  usually  described  as 
''denaturation."  Various  other  cases  of  anomalous 
adsorption  are  probably  to  be  referred  to  conditions  of  a 
similar  kind;  the  adsorbed  material  apparently  under- 
goes some  chemical  modification. 

A  further  fact  of  fundamental  biological  interest  is 
that  the  adsorbent  action  of  many  materials  has  a 
certain  specificity  or  selective  character;  i.e.,  the  action 
varies  from  adsorbent  to  adsorbent  independently  of 
the  latter's  state  of  subdivision.  This  phenomenon  has 
apparently  the  same  ultimate  basis  as  have  the  specific 
chemical  affinities  between  substances;  in  fact,  the 
distinction  between  adsorption  and  the  fomiation  of 
true  chemical  compounds  is  now  ver>'  generally  recog- 
nized as  ill  defined.''  The  phenomena  of  cohesion,  adhe- 
sion, and  capillarity  are  closely  related  to  adsoq)tion; 
thus  water  wets  (is  adsorbed  by)  certain  solid  surfaces, 

^  Freundlich  and  Losev,  Z.  physik.  Chem.,  XLIX  uyo?).  284. 
'  Cf.  Langmuir,  op.  cit.,  pp.  1900  IT.;   also  Journal  of  the  American 
Chemical  Society,  XL  (1918),  1361. 


78  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

but  not  others.  It  is  well  known  that  the  interfacial 
tension  between  an  adsorbing  surface  and  a  solution  of 
an  adsorbable  substance  is  a  direct  function  of  the  degree 
of  adsorption  of  the  latter. 

When  the  adsorbed  substances  are  of  low  molecular 
weight — e.g.,  in  homologous  series  of  alcohols,  organic 
acids,  or  similar  compounds — it  is  usually  found  that  the 
order  of  relative  adsorption  is  not  altered  by  altering 
the  adsorbent,  although  the  degree  of  adsorption  may 
vary  widely  with  the  different  adsorbents.  With  more 
complex  molecules,  however,  relations  of  an  apparently 
arbitrary  or  specific  kind  often  enter,  and  presumably  the 
relations  between  the  molecular  structure  or  configura- 
tion of  the  adsorbing  surface  and  that  of  the  adsorbed 
substance  then  become  important.  Specific  adsorptions, 
like  specific  chemical  combinations  (between  enzyme  and 
substrate,  or  antigen  and  anti-body)  are  thus  probably 
largely  dependent  on  similarities  of  chemical  configura- 
tion. Hence  a  good  adsorbent  for  one  substance  may 
be  a  poor  one  for  another.^  Freundlich  cites  various 
instances  illustrating  the  differences  between  the  adsorb- 
ent powers  of  different  materials  for  the  same  substance.^ 
Thus  charcoal  adsorbs  crystal  violet  20  times  as  effec- 
tively as  silk,  and  156  times  as  effectively  as  cotton  wool. 
He  found  that  different  adsorbents  usually  showed  the 
same  order  of  relative  adsorption  for  the  dyes  used; 
with  four  solid  adsorbents  the  general  order  of  adsorbent 
action  was  charcoal>wool>  silk  >  cotton,  but  the  ratios 
of  the  adsorption  constants  varied  with  different  dyes. 

^  Cf.  Bayliss,  op.  cit.,  p.  60,  for  instances  of  specific  adsorption;  also 
Bancroft's  Applied  Colloid  Chemistry,  p.  3. 

^  Freundlich,  K  a  pillar  chemie,  p.  155. 


PROTOPLAS.MIC  STRUCTURE  79 

Wohler  and  Plucldcmann'  found  that  iron  oxide  adsorljcd 
10  times  as  much  benzoic  acid  as  acetic  acid;  chromic 
oxide  adsorbed  both  about  equally;  while  i)hitinum 
sponge  adsorbed  more  acetic  than  benzoic,  but  both 
slightly.  According  to  Freundlich,  gelatine  adsorbs 
sugar  only  after  having  been  treated  with  fomialdehyde.* 
The  influence  of  the  specific  molecular  structure  of  the 
adsorbent  on  its  selective  adsorption  is  well  shown  in 
the  investigations  of  Marc.  A  crystalline  adsorbent, 
BaC03  (rhombic)  adsorbs  KXO3  (rhombic)  but  not, 
or  slightly,  NaN03  (hexagonal);  CaC03  (hexagonal) 
adsorbs  NaN03  but  not  KN03.^  These  observations 
throw  an  interesting  light  on  the  phenomena  of  crystal- 
lization; it  is  well  known  that  the  specific  molecular 
configuration  of  a  substance  determines  the  form  in 
which  it  cpy'stallizes,  as  originally  shown  by  Pasteur's 
observations  on  the  separation  of  kevo-  and  dextro- 
tartrate  in  separate  crystals  in  the  crystallization  of  the 
optically  inactive  solution.  Apparently  the  abstraction 
of  molecules  from  solution  and  their  deposition  to  form 
the  regular  solid  structure  or  cr}'stal  are  determined  by 
conditions  of  the  same  kind  as  those  detemiining  selec- 
tive adsorption.  Adsorption  of  molecules  at  the  surface 
of  the  crystal  is  a  preliminary  to  the  growth  of  the  latter; 
this  growth  is  evidently  dependent  on  mutual  apj)osition 
of  molecules  similar  in  configuration  and  dimensions  and 
with  their  axes  parallel.*'     In  organic  growth— another 

MVdhler  and  Pliiddcmann,  Z,  physik.  Chcni.,  LXII  (1908),  664. 
'  Freundlich,  op.  cU.,  p.  514. 

3  Marc,  Z.  physik.  Clicm.,  LXXXI  (1913),  641. 

4  Crystal  growth,  in  fact,  appears  to  afToni  the  clearest  cases  of 
specificity  in  adsorption. 


8o    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

type  of  specific  growth  and  form-determination — similar 
processes  are  almost  certainly  concerned. 

The  reversible  character  of  many  adsorption  processes 
is  a  property  of  great  biological  importance  and  appar- 
ently one  essential  to  certain  physiological  effects,  such 
as  narcosis,  which  are  universal  in  living  protoplasm. 
There  is  no  doubt  that  this  reversibility  also  plays  an 
essential  part  in  the  normal  chemical  processes  of  proto- 
plasm. The  displacement  of  one  adsorbed  compound  by 
another  of  greater  surface-activity  presupposes  reversible 
adsorption,  and  various  biological  instances  of  this  effect 
are  known.  Thus  an  adsorbed  enzyme  can  be  removed 
from  an  adsorbing  surface  by  adding  a  more  surface- 
active  substance;  e.g.,  rennin  adsorbed  by  charcoal  and 
added  to  milk  will  not  coagulate  the  latter,  but  on  the 
addition  of  saponin  the  rennin  is  set  free  and  causes 
coagulation.  A  solution  of  rennin  is  inactivated  by 
shaking  with  air,  but  not  if  saponin  is  present;  the  latter 
protects  the  enzyme  by  preventing  adsorption  at  the 
air-water  interface.^ 

Similar  cases  of  inactivation  by  shaking  are  cited 
by  Meltzer  and  Shaklee.^  Apparently  only  the  adsorbed 
enzyme  is  inactivated;  it  has  already  been  mentioned 
that  changes  of  physical  state  frequently  result  from  ad- 
sorption; Ramsden's  observation  that  proteins  can  be 
coagulated  by  shaking  with  air  is  an  instance  of  the  same 
phenomenon.^  Hence  the  prevention  of  adsorption 
through   the   presence   of   another   surface-active  com- 

'  Cf .  the  observations  of  Jahnson-Blom  (191 2),  and  Schmidt- 
Neilson  (1910),  cited  in  Bayliss'  Principles  of  General  Physiology,  p.  70. 

'Meltzer  and  Shaklee,  Amer.  Jour.  Physiology,  XXV  (1909),  81. 

sRamsden,  Z.  physik.  Chem.,  XL VII  (1904),  343. 


PROTOPLASMIC  STRUCTURK  8l 

pound  may  be  a  factor  in  preventing  physical  and 
chemical  alteration  in  li\'ing  protoplasm.  Preventive 
effects  of  this  kind  probably  form  a  chief  factor  in 
the  anaesthetic  action  of  surface-active  compounds,  as 
well  as  in  the  protective  action  which  they  often  ex- 
hibit (against  salt  action,  haemolysis,  or  mechanical  in- 
jury).' 

ADSORPTION   AND   DEPENDENT   PHENOMENA    IN 
COLLOIDAL   SYSTEMS 

In  general,  colloids  of  the  suspensoid  group  are  less 
readily  adsorbed  than  those  of  the  emulsoid  group,  in 
correspondence  with  the  fact  that  the  latter  are  usually 
surface-active,  the  former  not.  For  the  same  reason 
the  suspensoids  do  not  usually  act  as  emulsifying  agents, 
while  many  emulsoids  are  highly  effective  in  this  regard. 
The  distinction,  however,  is  not  absolute,  since  finely 
divided  insoluble  substances  of  various  kinds  may 
emulsify  oils  under  certain  conditions;^  what  is  essential 
is  that  the  material  should  collect  and  form  a  continuous 
layer  at  the  surface  between  the  phases. 

As  a  rule  proteins  are  surface-active;  their  solutions 
have  lower  surface- tensions  than  pure  water  and  they 
are  readily  adsorbed.  The  conditions  are,  however, 
complex;  the  degree  of  adsorption  may  \ary  with  the 
same  protein  according  to  its  state  of  subdivision  (which 
varies  with  the  salt  content)  or  according  to  the  H-ion 
concentration  of  the  solution;  the  latter  condition  deter- 
mines the  proximity  to  the  isoelectric  point  and  hence 

^  See  pp.  207  fl. 

^Cf.  Bancroft,  loc.  cit.;  Journal  of  Physical  Chemistry,  X\I 
(1912),  475. 


82  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

the  electrical  properties  of  the  particles,  a  factor  which 
influences  their  adsorption.^ 

Observations  on  the  relation  between  the  concen- 
tration of  proteins  in  solution  and  the  degree  of  their 
adsorption  give  many  abnormalities,  probably  referable 
chiefly  to  variations  in  the  aggregation  state.^  The 
particles  cohere  and  form  larger  aggregates  which  con- 
dense at  surfaces,  forming  films  of  modified  protein. 
Such  processes  are  largely  irreversible,  and  chemical 
change  probably  also  enters  as  a  factor;  the  changes 
in  the  properties  of  enzymes,  dyes,  and  other  colloidal 
compounds  in  adsorption  are  probably  to  be  thus 
explained.  Many  cases  of  abnormal  and  irreversible 
adsorption  belong  here;  such  abnormalities  are  especially 
characteristic  of  colloids  of  the  emulsoid  group.  The 
surface-activity  of  proteins,  and  the  readiness  with  which 
they  form  films,  filaments,  and  other  coherent  structures, 
at  the  surfaces  where  they  are  adsorbed,  are  undoubtedly 
properties  of  great  biological  importance;  and  we  may 
assume  that  in  the  deposition  of  proteins  in  a  solid  or 
semi-solid  state  to  form  the  more  permanent  structural 
elements  of  protoplasm  such  processes  play  a  chief  part. 
As  already  indicated,  it  seems  probable  that  specific 
adsorption,  a  process  apparently  based  on  the  tendency 
of  molecules  of  similar  configuration  to  cohere  or  coalesce 
to  form  larger  aggregates,  is  the  fundamental  factor 
underlying  the  specificity  of  growth  processes. 

As  already  pointed  out,  adsorption  may  furnish  the 
conditions  for  many  of  the  chemical  reactions  in  cells; 

^  Cf .  Christiansen,  cited  by  Pauli,  Colloid  Chemistry  of  Proteins, 
Philadelphia  (1922),  p.  89. 

2  Cf.  Hober,  op.  cit.,  pp.  217  flf. 


PROTOrLAS.MIC  STRUCTURE  83 

i.e.,  material  concentrated  or  condensed  at  the  proto- 
plasmic surfaces  may  in  this  manner  first  become  capable 
of  chemical  interaction.  In  a  recent  pa])er'  Hayliss 
gives  instances  showing  that  in  many  reactions  in  poly- 
phasic  systems  adsorption  is  the  initial  process  which 
forms  a  necessary'  preliminary  to  the  true  chemical  com- 
bination following. 

We  may  conclude  that  the  determination  and  control 
of  chemical  reactions  by  adsorption  are  universal  in 
living  protoplasm.  The  presence  of  colloidal  comj)lexes 
or  ''adsorption  compounds" — e.g.,  compounds  of  lecithin 
with  proteins,  such  as  lecithin-vitellin  (in  the  ethereal 
extract  of  egg  yolk)  and  jecorin  (dextrose  and  lecithin 
plus  protein) — is  frequent  in  organisms.  Inorganic 
salts  and  ions  are  probably  also  largely  present  in  a  con- 
dition of  adsorption;^  and  the  indications  are  that  the 
action  of  the  surface-active  pharmacological  compounds 
(especially  the  anaesthetics)  is  largely  so  determined. 
According  to  Loewe,  the  chief  relation  between  lipoids 
and  narcotic  compounds  is  one  of  adsorption,*'  although 
the  relative  solubilities  of  these  compounds  in  the 
different  protoplasmic  phases  (partition-coefficients) 
probably  also  enter  as  an  important  factor  in  narcotic 
action.'' 

The  promotion  of  chemical  action  by  adsoq)tion 
is  often  called  ''adsorption-catalysis."  Well-known 
examples  are  the  formation  of  U^SO^  from  SO,  in  the 
presence  of  platinum,  the  reduction  of  various  compounds 

^  Proceedings  of  the  Royal  Society,  B,  LXXXIV  (1911),  81. 
'  Cf .  Pauli,  loc.  cit. 

3  Loewe,  Biochem.  Z.,  LVII  (1913),  161;  cf.  pp.  2cx)  IT. 

4  See  chap,  ix  for  the  relation  of  adsorption  to  narcosis. 


84     PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

by  hydrogen  in  the  presence  of  platinum,  and  the  oxida- 
tion of  compounds  by  blood-charcoal  (oxalic  acid,  etc.). 
The  combination  of  tannin  with  leather  is  a  good  illus- 
tration of  the  determination  of  a  chemical  reaction  by 
a  previous  adsorption;  the  tannin  is  first  adsorbed,  then 
it  combines.  The  same  condition  is  shown  in  the  union 
of  dyes  with  heat-denatured  egg-white;  the  process 
is  at  first  readily  reversible  (by  acid),  but  not  later, 
indicating  that  the  first  stage  of  the  process  is  a  close 
contact  or  adhesion,  which  is  then  followed  by  chemical 
combination.^  The  toxin-antitoxin  reactions  and  the 
opsonin  reaction  with  leucocytes  are  further  biological 
instances  of  a  similar  kind.  According  to  Morgenroth, 
tetanus  toxin  is  taken  up  or  attached  by  living  cells 
at  8°,  but  does  not  become  active  until  20°.  In  the  action 
of  enz}Tiies  adsorption  processes  play  an  important  part, 
as  already  indicated.^ 

INFLUENCE    OF   ELECTRICAL   STATE    OF   SURFACE 

ON   ADSORPTION 

The  relations  of  electrostatic  attraction  or  repulsion 
between  the  charged  surface  of  the  adsorbent  and  the 
charge  on  the  particles  of  the  dissolved  substance  consti- 
tute a  factor  of  decisive  importance  in  many  adsorption 
processes.  For  example,  acid  dyes  (whose  colloidal 
particles  are  negatively  charged)  are  as  a  class  more 
readily  adsorbed  by  suspended  alumina  (with  positive 
particles)  than  by  kaolin,  a  silicate  with  negative 
particles,  and  vice  versa.  Color  bases  show  the  reverse 
behavior,   being   adsorbed   by   substances   which   form 

^  Unpublished  observations  of  my  own. 

2  Cf.  the  data  and  discussion  in  Bayliss'  textbook,  p.  324. 


PROTOPLASMIC  STRUCTrpi-:         85 

negatively  charged  surfaces;  e.g.,  silicates,  carbon,  and 
adsorbents  of  chemically  acid  character,  but  not  by 
hydrates  like  alumina  or  other  positive  adsorbents.' 
Suspensoids  of  heat-denatured  allnimin  show  the  same 
behavior;  when  the  particles  are  made  positive  by  the 
addition  of  a  little  acid  they  become  adsorbents  for 
acid  dyes,  which  also  cause  precipitation;  while  in  the 
negative  condition,  i.e.,  on  the  alkaHne  side  of  the  iso- 
electric point,  they  are  precipitated  by  (and  adsorb) 
basic  but  not  acid  dyes.  The  mutual  precipitation  of 
oppositely  charged  colloidal  solutions  when  mixed  in 
suitable  proportions  is  an  example  of  the  same  phe- 
nomenon. 

The  importance  of  the  electrical  factor  in  the  general 
behavior  of  colloids  is  indicated  by  the  remarkable 
changes  in  adsorptive  and  chemical  properties  which 
a  given  protein  exhibits  when  the  H-ion  concentration 
of  the  solution  passes  from  one  side  of  the  isoelectric  point 
to  the  other.  On  the  acid  side  precipitation  is  induced 
by  the  anions  of  an  added  electrolyte,  on  the  alkaline 
side  by  the  cations,  as  Hardy  first  showed  in  the  case  of 
heat-modified  egg-albumin.''  Recently  the  rehition 
between  the  charged  condition  of  the  protein  aggregates 
and  their  chemical  and  other  behavior  has  been  investi- 
gated in  much  detail  by  Loeb,^  who  has  detennined  many 
striking  correlations  between  the  physical  and  the 
chemical  properties  of  proteins  at  varying  Il-ion  con- 

'  Cf.  Michaelis, P/m/A'a//ir/;c  Chcmic  iiml  J/<7//c/;/, edited  by  Kt)ran\i 

and  Richter,  Leipzig,  II  (1908),  341. 

*W.  B.  Hardy,  Proceedings  of  the  Royal  Society,  LX\  1  u-^yy.  »»^- 
3  For  a  summary  of  these  important  in\cstigations  cf.  Locb's  recent 

book  Proteins  and  the  Theory  of  Colloidal  Be/uivior,  New  York,  192^. 


86    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

centrations.  As  Pauli^  also  has  pointed  out,  many 
properties  (viscosity,  osmotic  pressure,  refractive  index, 
precipitability  by  alcohol)  pass  through  a  minimum 
which  is  coincident  with  the  isoelectric  point. 

In  all  colloids  the  electrical  factor  plays  a  special 
part  in  changes  of  aggregation  state  or  dispersion.  In 
precipitation  by  electrolytes  adsorption  processes  enter; 
one  or  the  other  ion  is  adsorbed  predominantly,  i.e., 
the  ion  of  opposite  sign  to  the  colloidal  particle;  accord- 
ingly this  ion  is  the  precipitant.  In  general  the  more 
readily  adsorbed  an  electrolyte  is,  the  more  effective  it  is 
as  a  precipitating  agent.  Freundlich  has  shown  this 
clearly  for  the  salts  of  a  number  of  organic  bases.^ 
The  relative  precipitating  effectiveness  of  the  several 
salts,  with  colloidal  arsenious  sulphide,  is  shown  in  the 
following  table: 

c  ,  Precipitating 

^^*''  Concentration 

Aniline  chloride 4.1 

P-chloraniline  chloride 2.2 

Strychnine  nitrate o. 39 

Morphine  chloride o. 36 

Neufuchsin o.  30 

The  order  of  precipitating  concentrations  is  the 
reverse  of  the  order  of  relative  adsorption. 

Theoretically  the  two  ions  of  an  electrolyte  should 
have  different  adsorption  constants  in  relation  to  an 
adsorbing  surface.  The  nature  and  quantity  of  the 
ions  adsorbed  will  influence  the  electrical  conditions  at 
the  interface,  and,  secondarily,  all  processes  in  which 
these  conditions  are  a  factor,  such  as  colloidal  stability, 

I  Cf.  W.  Pauli,  loc.  cit. 

^  Kolloid-Z.,  I  (1907),  328;  Kapillarchemie,  p.  351. 


PROrOPLAS]\IIC  STRUCTURE  87 

state  of  dispersion,  cataphoresis  and  electrical  endosmosc, 
and  catalytic  action.  The  action  of  electrolytes  on 
colloids  shows  many  indications  of  adsorption  effects; 
those  ions  which  other  evidence  indicates  are  in  general 
the  most  strongly  adsorbed  (H,  OH,  pol>'A'alent  cations) 
have  a  correspondingly  marked  influence  on  the  colloirlal 
state.  The  influence  of  adsorption  is  shown  with 
especial  distinctness  in  the  action  of  salts  on  ])r()tein 
solutions,  as  Pauli's  work  has  especially  shown;  the 
characteristic  curves  relating  temperatures  of  heat- 
coagulation,  melting  points  of  gels,  and  precipitability 
by  alcohol  to  concentration  of  salt  (when  the  salt  is 
present  in  excess  of  that  required  to  form  stoichiometric 
compounds)  are  clearly  of  the  adsorjDtion  t^-pe/  The 
same  is  true  for  the  influence  of  salts  on  the  osmotic 
pressure  of  protein  solutions.^ 

Apparently,  in  all  processes  where  surface  effects  are 
concerned,  the  different  salts  of  the  same  metal  dilTer  in 
their  action  according  to  the  nature  of  their  anions; 
according  to  Rontgen  and  Schneider^  the  order  of  rela- 
tive adsorption  of  anions  is  S04<Cl<Br  and  X03<I; 
this  series  corresponds  to  the  characteristic  lyotropic 
series  of  Hofmeister,  which  is  shown  not  only  in  the 
above-cited  work  on  proteins  and  in  many  of  the  physio- 
logical effects  produced  by  salts  but  also  in  various 
purely   physical   phenomena   involving   surface    factors 

'  Cf.  Pauli's  book  {loc.  cit.)  for  references. 

2  The  data  in  my  paper  (American  Journal  of  Physiology,  XX  (1907), 
127)  show  a  relatively  great  depressant  action  on  osmotic  pressure  for 
low  concentrations  of  salts  and  a  cur\e  corresponding  to  the  adsor]nion 
type. 

3  Rontgen  and  Schneider,  Ann.  Physik.,  XXIX  (1SS6),  165. 


88    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

(influence  of  salts  on  surface   tension,   solubility,  vis- 
cosity, catalytic  action,  etc.).^ 

ADSORPTION   OF   IONS 

The  difference  between  the  adsorbability  of  the  two 
ions  of  an  electrolyte  implies  an  influence  on  the  potential 
difference  at  the  phase-boundary;  the  surface  receives 
the  charge  of  the  raore  adsorbable  ion  and  the  adjacent 
layer  of  solution  the  opposite  charge.  Potentials 
arising  in  this  way  have  been  called  "adsorption  poten- 
tials" by  Freundlich,^  and  they  undoubtedly  play  an 
important  part  in  colloidal  phenomena,  since  the  altera- 
tion of  the  surface  charge  is  a  chief  factor  in  the  changes 
of  aggregation-state  and  other  phenomena  characteristic 
of  colloids.  Adsorption  potentials  may  also  be  of  great 
importance  in  influencing  the  character  of  the  chemical 
changes  occurring  under  the  catalytic  influence  of 
surfaces. 

There  are  many  indications  that  the  ions  of  water, 
OH  and  H,  are  among  the  most  readily  adsorbed  ions. 
This  property  is  of  special  biological  importance,  since 
most  forms  of  protoplasm  are  highly  sensitive  to  varia- 
tions in  the  concentration  of  these  ions;  and  in  certain 
cases  this  sensitivity  has  become  a  regulatory  factor  of 
the  utmost  delicacy.     Free  organic  acids  and  bases  are 

^  For  a  summary  of  the  physical  effects  of  salts  showing  the  lyotropic 
series  cf.  Hober,  op.  cit.,  p.  310. 

^  According  to  Freundlich  the  adsorption  potential  is  not  the  poten- 
tial between  the  interior  of  the  solid  phase  and  the  adjoining  solution, 
but  that  between  an  adhering  immobile  layer  of  solution  and  the  mobile 
layer  adjoining.  Cf.  Kapillarchemie,  p.  243;  also  Report  on  the  Physics 
and  Chemistry  of  Colloids  by  the  Faraday  Society  and  the  Physical 
Society  of  London  (192 1),  p.  146. 


PROTOPLASMIC  STRUCTURE  89 

as  a  rule  more  readily  adsorbed  than  their  salts.  Many 
organic  acids  (the  lower  members  of  the  fatty  series) 
are  highly  effective  in  lowering  surface-tension,  while 
their  salts  have  little  influence;  this  effect,  however, 
may  be  in  large  part  attributable  to  the  undissociated 
molecules.  As  a  class,  acids  have  a  marked  effect  on 
the  surface  charges  of  inclilTerent  solid  substances, 
tending  to  make  these  surfaces  positive;  similarly  bases 
make  them  negative.  Both  effects  appear  in  very  low 
concentrations  (Perrin)^  and  are  undoubtedly  due  to 
H  and  OH  ions,  respectively.  The  fact  that  adsorbent 
surfaces  of  the  most  widely  varying  chemical  composi- 
tion (carbon,  hydrocarbons,  silicates,  oxides,  metals) 
are  thus  affected  indicates  that  adsor]:)tion  rather  than 
chemical  combination  in  stoichiometric  proportions  lies 
at  the  basis  of  the  effect.  A  slight  change  in  H  and  OH 
concentration  may  thus  have  a  very  marked  effect 
upon  the  potential  difference  across  a  surface;  this  is 
well  shown  in  the  curves  given  by  Haber  and  Klemensie- 
wicz,"*  and  in  the  results  of  Perrin.^  The  great  effective- 
ness of  the  H-ion  as  a  precipitant  for  suspensions  of 
indifferent  substances  probably  dej)ends  on  its  high 
adsorbability  as  well  as  on  its  high  velocity  and  special 
chemical  properties. 

At  a  certain  concentration  where  OH  and  H-ions  are 
adsorbed  in  certain  proportions  the  surfaces  will  be 
electrically  neutral;   this  condition  defines  the  isoelectric 

'  Cf.  Pcrrin,  Jour.  Chini.  Phys.,  II  (1904),  6or. 

*  Haber  and  Klcmcnsicwicz,  Z.  phys'ik.  Cheni.,  LX\  II  UiJOq),  i^S- 

3  See  especially  Pcrrin's  curve  for  naphthalene,  rcprtxluccd  in 
Freundlich's  KapiUarchcmic,  p.  236.  Ellis  also  describes  this  ctTccl  in 
the  cataphoresis  of  oil  droplets,  Z.  physik.  CJtcm.,  CXWIII  (191 1),  321. 


90    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

point.  The  H-ion  concentration  corresponding  to  this 
neutral  position  varies  according  to  the  special  chemical 
character  of  the  material  and  its  adsorbent  properties. 

Various  chemical  effects  apparently  depending  on 
unequal  adsorption  of  ions  are  described  in  Freundlich's 
book;  frequently  these  appear  to  be  consequences  of  the 
displacement  of  one  ion  from  an  adsorbent  surface  by 
another  which  is  more  readily  adsorbed.  For  example, 
many  basic  dyes  (crystal  violet  or  basic  fuchsin)  are 
chlorides  of  organic  color-bases;  when  these  dyes  are 
adsorbed  by  charcoal,  a  large  part  of  the  combined 
chloride  goes  into  solution  as  inorganic  chloride.  This 
result  is  explained  by  FreundHch  as  due  to  the  high 
adsorbability  of  the  color  cation  (dye-HCl  =  dye-H+ 
and  Cl~)  which  displaces  from  the  adsorbent  the  adsorbed 
cation;'  according  to  this  view  the  chemical  splitting  is 
due  to  the  unequal  adsorbability  of  the  two  ions.  The 
phenomenon  may,  however,  be  regarded  as  a  consequence 
of  the  high  adsorbability  of  the  free  base,  which  is  present 
in  the  solution  in  consequence  of  partial  hydrolysis;  this 
base  is  removed,  leaving  the  chloride  in  solution.^  It  is 
known  that  many  organic  free  bases  are  more  highly  sur- 
face-active (adsorbed)  than  the  salts;  thus  Traube  points 
out  that  the  surface-tension  of  solutions  of  hydrochlorides 
of  the  alkaloids,  cocain,  atropin,  and  quinine  is  lowered 
by  adding  a  little  alkali,  an  effect  due  to  the  liberation 
of  the  free  base;^  the  latter  will  tend  to  be  adsorbed  and 
the  hydrolysis  will  be  promoted.     The   separation  of 

^  Freundlich,  op.  ciL,  p.  i68. 

'  Cf.  Michaelis,  Arch.  ges.  Physiol.,  XCVII  (1903),  634. 

3  Traube,  Kolloidchem.  Beihefte,  III  (191 2),  237;  cf.  also  Hober, 
op.  cU.,  p.  215. 


PROTOPLASMIC  STRUCTURE  91 

dyes  on  adsorbing  surfaces  in  an  insoluble  fomi  and  the 
^'denaturation"  of  proteins  on  surfaces  are  apparently 
phenomena  of  the  same  general  kind;  ads(jrption  will 
promote  hydrolysis  or  other  chemical  alteration  in  a 
compound  if  any  reaction-product  is  more  readily 
adsorbed  than  the  original  compound.  From  this 
point  of  view  the  general  kinetics  of  adsorption-catalysis 
appear  in  a  clearer  light. 

The  heavy  metal  ions  and  the  ions  of  trivalent 
metals  appear  to  be  adsorbed  with  especial  readiness  in 
many  cases,  and  the  solutions  of  their  salts  have  a  corre- 
spondingly great  influence  on  the  surface  charge  of  col- 
loidal particles  and  of  porous  partitions.  In  the  case  of 
suspended  oil  drops,  ElHs^  found  the  following  concen- 
trations of  three  chlorides  to  be  equally  effective  in 
removing  the  charge;  i.e.,  in  rendering  the  particles 
electrically  neutral. 

■K/r  ^         T  •*  Relative 

Mols.pcrLitre  Concentration 

AICI3 0.00026  I 

CuCla 0.00S9  ca.  40 

NaCl 0.40  ca.  1600 

The  relative  actions  of  Na,  Cu,  and  Al  are  approxi- 
mately as  I  to  40  to  1,600,  indicating  a  rapid  increase 
of  action  with  increase  of  valence.  The  same  rule  is 
found  in  the  precipitation  of  suspensoid  colloids  by 
electrolytes  (rule  of  Schulze  and  Hardy),  and  indicates 

^Ridsdale  Ellis,  Z.  physik.  Chem.,  LXXVIII  (1912),  321-  I^^b's 
recent  study  of  the  effects  of  ions  in  altering  the  charge  on  suspended 
collodion  particles  gives  a  sunilar  result  (/.  Gen.  Physiol.,  V  [1922J,  109). 
In  this  case  the  collodion  particles  undergo  precipitition  when  the  P.D. 
against  the  medium  falls  below  16  millivolts.  Bacteria  are  agglutinated 
at  15  millivolts  accordmg  to  Northrop  and  de  Kruif  (loc.  cit.). 


92     PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

that  a  relatively  great  adsorption  of  polyvalent  ions  is  a 
general  rule.  The  relative  effectiveness  of  polyvalent 
cations  in  certain  characteristic  physiological  effects, 
e.g.,  ion-antagonism,  is  of  a  corresponding  order,  indicat- 
ing that  in  such  cases  the  ions  act  by  adsorption  at  the 
structural  surfaces  of  the  living  system.  Thus  Al  and 
Cr  ions  greatly  prolong  the  activity  of  cilia  in  isotonic 
NaCl  solution  when  present  in  concentrations  of  less 
than  M/ 100,000.^ 

It  should  be  pointed  out  that  even  if  the  adsorption 
constants  of  mono-,  di-,  and  trivalent  ions  were  equal, 
the  trivalent  ions  should  be  effective  in  less  than  a  third 
of  the  concentration  of  the  monovalent  ions,  because, 
on  account  of  the  characteristic  form  of  the  adsorption 
curve,  the  ratio  between  the  quantity  adsorbed  and  the 
quantity  remaining  in  solution  is  much  higher  in  dilute 
than  in  concentrated  solution;  hence  sufficient  trivalent 
ions  to  neutralize  the  surface  charge  may  be  adsorbed 
from  extremely  dilute  solution.  This  is  Freundlich's 
explanation  of  Schulze's  rule.''  Whetham's  explanation, 
based  on  chances,^  is  probably  insufficient,  although 
purely  mathematical  considerations  would  indicate 
that  the  statistical  conditions  to  which  he  calls  atten- 
tion must  play  a  part  in  the  total  effect.  The  ratio 
between  the  effective  concentrations  of  Al  and  Na  in  the 
above-cited  experiments  seems,  however,  too  great  to 
be  accounted  for  on  this  ground  alone,  and  a  high  degree 
of  adsorption  of  polyvalent  cations  must  apparently  be 
assumed. 

^  R.  S.  Lillie,  American  Journal  of  Physiology,  X  (1904),  430. 

2  Freundlich,  Z.  physik.  Chem.,  LXXIII  (1910),  385. 

3  Whetham,  Theory  of  Solution,  p.  396. 


PROTOPLASMIC  STRUCTURE  93 

The  importance  of  adsorinion-potcntials  is  shown 
most  clearly  in  the  phenomena  of  electrical  cndosmosc, 
which  are  of  great  physiological  im])()rtance  and  will  be 
considered  briefly  below.  The  marked  influence  which 
slight  quantities  of  acid  and  alkali  have  in  altering  the 
phase-boundary  potentials,  especially  in  the  neighbor- 
hood of  the  isoelectric  point,  is  a  fact  of  special  biological 
interest.  Near  this  point  the  effect  of  variations  in  the 
H-ion  concentration  upon  the  phase-boundary  potentials 
is  at  its  maximum;  farther  from  the  isoelectric  point 
the  difference  caused  by  a  given  change  in  the  H-ion 
concentration  is  relatively  slight.' 

The  reactions  of  the  tissue  fluids  in  higher  animals  arc 
slightly  on  the  alkaline  side  of  neutrality,  and  the  reaction 
of  the  living  protoplasm  (because  of  the  higher  tension 
of  CO2  within  the  cell)  is  presumably  somewhat  less 
alkaline  and  is  probably  not  far  from  the  isoelectric 
point  of  some  of  the  structural  proteins.  Hence  slight 
variations  of  the  H-ion  concentration  within  the  cell 
should  have  a  correspondingly  great  effect  upon  the 
boundary -potentials  of  the  corresponding  cell-structures. 
Variations  in  the  H-ion  concentration  of  the  cell-medium 
would  affect  first  of  all  the  boundar}--potential  of  the 
cell  as  a  whole;  i.e.,  that  existing  across  the  plasma 
membrane,  and  this  is  probabh'  the  chief  reason  win- 
living  tissues  are  frequently  so  sensitive  to  changes  in  the 
external  H-ion  concentration.  As  already  j^ointed  out. 
this  sensitivity  has  in  some  cases  become  the  controlling 
factor  in  regulator}-  processes  of  vital  importance  to 
the  whole  organism,  as  in  the  respiratory  nerve  cells  of 
vertebrates,    which    show    an    accelerated    rhythm    in 

^  C/.  Ilabcr  and  Klcmcnsiewicz,  loc.  cil. 


94  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

response  to  an  extremely  slight  rise  of  acidity  due  to 
increase  in  the  CO2  of  the  blood. 

ELECTRICAL   ENDOSMOSE 

Certain  physical  phenomena  of  great  biological 
interest,  having  similar  relations  to  the  charged  char- 
acter of  the  interphasic  surfaces,  are  those  classed  as 
electrical  endosmose.  The  essential  phenomenon  is 
the  transfer  of  fluids  with  or  against  an  electric  current 
traversing  a  porous  partition  immersed  in  an  electrolyte 
solution.  The  fundamental  conditions  of  this  transport 
are  the  same  as  those  determining  the  electrical  con- 
vection of  colloidal  particles  or  emulsion  droplets, 
except  that  in  electrical  endosmose  the  continuous  fluid 
phase  is  the  mobile  one,  the  solid  phase  which  forms 
the  substance  of  the  partition  being  fixed  in  position. 
Colloidal  gels  interposed  in  the  path  of  a  current  exhibit 
this  phenomenon,  and  it  is  well  known  in  protoplasmic 
systems.^  There  is  no  question  but  that  effects  of  the 
same  kind  must  occur  normally  in  living  matter,  since 
the  latter,  during  functional  activity  at  least,  is  continu- 
ally being  traversed  by  the  currents  of  the  bioelectric 
circuits;  and  it  seems  probable  that  electrical  endosmose 
plays  a  special  role  in  the  processes  of  secretion  and 
adsorption,    as    suggested    by    various    physiologists.'' 

^  For  example,  Hermann  describes  experiments  showing  the  trans- 
port of  water  through  tissues  (muscle  and  nerves)  in  the  direction  of 
the  positive  stream  when  a  constant  current  is  passed  through  the 
tissue  {Arch.  ges.  Physiol.,  LXVII  [1897],  240). 

^Engehnann,  Arch.  ges.  Physiol.,  VI  (1872),  97;  Waymouth  Reid, 
Phil.  Trans.,  Series  B,  CXCII  (1900),  239;  Hober,  Arch.  ges.  Physiol, 
CI  (1904),  607;  cf,  also  my  recent  paper  in  Biological  Bulletin,  XXXIII 
(1917),  135,  i7off. 


PROTOPLASMIC  STRUCTURE  95 

At  present,  however,  our  knowledge  is  insufTicicnt  for 
any  final  estimate  of  its  physiological  importance. 

Since  the  effect  depends  upon  the  potential  difTercnce 
between  the  walls  of  the  pores  and  the  mobile  fluid  layer 
adjoining,  all  conditions  that  influence  this  potential 
difference  affect  the  character  of  the  movement.  The 
rate  of  the  movement  or  its  direction  or  both  mav  be 
thus  affected.  The  effects  of  salts,  acids,  and  alkalies 
are  well  illustrated  in  Perrin's  investigations  publishi-d 
in  1904.^  The  following  table  gives  the  results  of  a 
typical  experiment.  The  diaphragm  consisted  of  naph- 
thalene, and  varying  solutions  of  HCl  and  KOH  were 
used: 

Solution  H.  cone,  (n)        OH  cone,  (n)    D^JphSgrn  ^^^ 

n/ 50  HCl 2X10-2        5X10-^3  -f-  38  to  anode 

n/ 1 00  HCl 10-2  10-^2  _|_  39  to  anode 

n/iooo  HCl.  .  .  .   10-3  10-"  +  28  to  anode 

n/ 5000  HCl ...  .     2X10-4        5X10-"  +  3  to  anode 

n/5oooK0H..,     5X10-^^       2X10-4  —  29  to  cathode 

n/ioooKOH...   iQ-"  10-3  —  60  to  cathode 

n/50  KOH 5X 10-13       2X10-2  —  60  to  cathode 

This  experiment  and  others  of  a  similar  kind  show  that 
when  a  current  of  given  intensity  is  passed  through  a 
partition,  the  rate  and  direction  of  transport  are  deter- 
mined by  the  charge  of  the  partition  substance,  and 
that  this  varies  in  a  definite  manner  with  the  nature 
and  concentration  of  the  ions  present. 

Perrin  also  showed  that  the  isoelectric  point  varied 
with  the  nature  of  the  diaphragm;  thus  j)artitions  of 
iodoform  and  glass  were  persistently  negative,  while 
those  of  BaCOj  and  CrCl3  were  positive.     The  electro- 

*  Perrin,  /.  Chim.  Phys.,  H  (1904),  601. 


96    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

positivity  of  any  surface,  whatever  its  chemical  composi- 
tion, was  invariably  increased  by  adding  monovalent 
acid  to  the  solution,  and  decreased  by  adding  monovalent 
base.  Polyvalent  ions  were  very  effective,  reversing 
the  sign  of  the  partition-charge  in  extremely  low  con- 
centrations; e.g.,  for  a  partition  of  chromic  chloride 
these  results  were  found. 

So'^'i-  D^fem  Flow 

Water  slightly  acid +  59 

Same-h.ooi  n  KjFe  (CN)6 ...  +  2 

Same-|-.o2  n  K3Fe  (CN)6.  ...  —  20  (reversal) 

Freundlich^  calculated  from  Perrin's  data  the  con- 
centration of  salts  (millimols  per  litre)  required  to  reduce 
by  50  per  cent  the  endosmose  through  positive  and  nega- 
tive partitions,  respectively,  and  obtained  the  following 
results. 

I.  CrCl3  (positive)  Cone,  (millimols  per  litre)  for 

Solution  1/2  velocity 

Dil.  acid+KBr 60 

Same-f  MgS04 i 

Same-l-K3Fe(CN)6 o.  i 

II.  Carborundum  (negative)  Cone,  for  1/2  velocity 
Solution 

Dil.  alkali-hNaBr 50 

Same-hBa(N03)2 2 

Same-|-La(N03)3 o.  i 

The  effect  thus  increases  very  rapidly,  in  accord- 
ance with  Schulze's  rule,  with  increase  in  the  valence 
of  the  active  ion,  which  is  always  that  having  the  opposite 
sign  to  that  of  the  partition.     Ellissafoff^  in  an  investiga- 

^  K  a  pillar  chemie,  p.  238. 

^  EllissafoJBf,  Z.  physik.  Chem.,  LXXDC  (191 2),  385. 


PROTOPLASMIC  STRUCTURE  07 

tion  with  glass  and  quartz  capillaries  also  found  the 
Perrin-Schulze  valence  rule  to  hold  for  alkali  and  alkali 
earth  salts,  but  heavy  metals  (Hg,  Ag)  were  more 
active  than  corresponded  to  their  valence;  organic 
cations  (morphine,  neufuchsin)  were  also  highly  active. 
Reversals  with  Th(N03)4  and  methyl  \iolet  were 
observed,  but  not  with  acids  up  to  n/iooo;  no  higher 
concentrations  were  used.^ 

^  A  general  review  by  T.  B.  Briggs  in  the  Journal  of  Physical  Chan- 
istry  for  191 7  (XXI,  198,  and  XXII,  256)  gives  a  full  review  of  the 
subject  of  electrical  endosmose.  Recently  its  bearing  on  physiological 
phenomena  and  its  relation  to  cases  of  anomalous  osmosis  have  been 
considered  in  an  important  series  of  papers  by  J.  Locb  {J.  Gen.  Physiol. ^ 
II  [1920],  p.  557,  and  later  papers  in  the  same  journal).  For  the  action 
of  ions  see  further,  A.  Gyemant,  "Elektrocndosmose  und  loncnadsoq)- 
tion,"  Kolloid-Z.,  XXVIII  (1921),  103. 


I 


CHAPTER  VI 

PROTOPLASMIC  STRVCTVRE— Continued:    PERMEA- 
BILITY AND  OTHER  PROPERTIES  OF 
PROTOPLASMIC  MEMBRANES 

We  have  seen  that  the  stabiHty  of  emulsion  systems 
and  many  of  their  essential  properties  are  determined  by 
the  presence  of  thin  interfacial  films.  In  the  formation 
of  these  films,  and  in  the  determination  of  their  special 
properties,  electrical  and  other  factors  enter,  of  a  kind 
characteristic  of  boundary  surfaces  in  general.  In 
general,  it  may  be  said  that  heterogeneous  mixtures 
containing  substances  that  influence  the  surface-tension 
or  the  electrical  polarization  at  the  phase-boundaries 
tend  to  reach  a  state  of  equilibrium  in  which  they  have 
what  may  be  called  a  ''structure";  i.e.,  a  more  or  less 
orderly  and  definite  distribution  of  the  components. 
The  gathering  of  surface-active  compounds  at  the 
phase-boundaries,  in  conformity  with  the  principle 
of  Gibbs  and  J.  J.  Thomson,  is  a  chief  factor  determining 
the  character  of  this  distribution;  and  the  latter  second- 
arily determines  the  character  of  the  chemical  changes 
occurring  in  the  system.  Living  protoplasm  is  an 
example  of  a  heterogeneous  system  in  which  the  control 
of  chemical  change  by  structural  conditions  has  reached 
perhaps  its  highest  development. 

Not  only  are  the  structural  elements  of  protoplasm 
(alveoli,  nuclei,  colloidal  particles,  fibrils)  bounded  by 
surfaces  at  which  adsorption  and  chemical  change 
occur,  but  the  whole  mass  of  protoplasm,   the  Hving 

98 


TROTOPLAS.MIC  STRUCTURE  99 

cell,  is  similarly  bounded.  Suspensions  of  living  cells — 
suspensions  of  blood  corpuscles,  eggs,  spermatozoa, 
bacteria,  or  yeast — in  their  normal  aqueous  media 
may  be  regarded  as  similar  in  many  respects  to  emulsions. 
Each  cell  is  a  small  discrete  particle  with  a  surface- 
tension  and  an  electrical  potential-difference  against  its 
medium.  The  existence  of  this  potential  is  shown  in 
convection  experiments;  just  as  oil  droplets  migrate  to 
the  anode  in  an  electrical  field,  so  do  suspended  living 
cells;  each  cell,  although  living  and  highly  differentiated 
internally,  behaves  in  this  respect  like  a  negatively  charged 
colloidal  particle.  As  in  the  case  of  a  suspended  oil  droplet, 
the  sign  of  the  charge  carried  by  the  living  particle  may  be 
changed  by  acids  or  polyvalent  ions;  and  like  colloidal 
particles  in  general  the  cells  may  be  precipitated  from 
suspension  (or  agglutinated)  under  various  conditions.* 

Red  blood  corpuscles  travel  in  neutral  media  like 
isotonic  sugar  solution  to  the  anode,  thus  showing  the 
presence  of  a  negative  surface  charge;  by  passing  CO, 
through  the  media  or  adding  weak  acids,  the  sign  of  the 
charge  may  be  reversed;  the  corpuscles  then  become 
positive  or  cathodic.^  At  an  intermediate  concentration 
the  charge  is  abolished  (isoelectric  point);  and  it  is 
interesting  to  note  that  at  this  point  the  cor])Uscle  tends 
to  break  down  or  undergo  hcemolysis.^     This  fact  is  of 

^  For  data  and  references  in  this  field,  cf.  Ilohcr's  Physik.  Chnnie 
d.  Zelle,  pp.  247,  300,  4<S3,  and  599.  ]Morc  recently  the  cata|)horcsis  of 
bacteria  and  their  agglutination  by  electrolytes  and  oUicr  substances  has 
been  studied  by  Northrop  and  De  Kruif  (J.  Gen.  Physiol.,  IV  (192:], 
629,  639,  and  655).  • 

^Hober,  Arch.  ges.  Physiol.,  CI  (1904),  627;  CII,  196. 

3  Michaelis  and  Takahashi,  Biochcm.  Zeitschrifl,  XXIX  (igio),  430- 
The  isoelectric  point  is  also  the  optimum  for  agglutination;  cf.  C.  R. 
Coulter,  Jour.  Gen.  Physiol.,  Ill  (1920),  309. 


lOO    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

special  interest  as  indicating  the  importance  of  electrical 
factors  in  the  structural  stability  of  the  protoplasmic 
surface  layer,  and  suggests  a  reason  why  depolarizing 
influences  have  in  general  a  stimulating  action  on  irritable 
cells.  The  relations  between  structural  change  and 
stimulation  will  be  considered  in  more  detail  later. 

Hober  and  Kozawa^  found  this  isoelectric  point  to 
vary  for  different  species  of  corpuscles  and  to  be  char- 
acteristic for  a  particular  species;  i.e.,  certain  corpuscles 
are  more  readily  made  positive  than  others  by  H  ions 
and  polyvalent  ions;  thus  the  corpuscles  of  rabbits  and 
guinea  pigs  were  found  to  require  the  least  H-ion  con- 
centration for  reversal  and  those  of  the  ox  and  pig  the 
highest;  those  of  the  dog,  cat,  goat,  and  man  were 
intermediate. 

Animal  Isoelectric  Point  (PH) 

Rabbit Between  t,.8  and  3.4 

Guinea  pig ca.  3.4 

Man  (and  cat) ca.  3.13 

Dog Between  3.13  and  2.98 

Sheep Between  2.98  and  2.77 

Pig ca.  2.77 

The  relative  order  with  La  ions  was  the  same.  Such 
differences  are  to  be  referred  to  the  specific  peculiarities 
of  structure,  composition,  or  permeability  characteristic 
of  each  kind  of  corpuscle. 

In  their  general  or  common  features,  these  phe- 
nomena indicate  that  the  behavior  of  the  protoplasmic 
free  surface  with  ref^ence  to  the  ions  present  in  the 
medium  resembles  that  of  the  surface  of  an  individual 
oil-droplet  in  an  emulsion.     It  may  be  assumed  that 

^  Hober  and  Kozawa,  Biochem.  Zeitschrijt,  LX  (1914),  146. 


PROTOPLASMIC  STRUCTURE  loi 

the  external  surface  of  the  cell  is  not  pecuhar  in  this 
respect,  and  that  other  protoplasmic  interfaces  (those 
within  the  cell)  have  similar  properties.  Film-fomiation, 
variations  of  electrical  polarization,  and  dependent 
phenomena  are  thus  to  be  regarded  as  constant  features 
of  the  processes  at  such  interfaces;  e.g.,  at  the  surfaces 
of  contractile  fibrils,  neuraxones,  vacuoles,  nuclei, 
alveoH,  and  other  protoplasmic  structures.  Secondary 
effects  peculiar  to  living  protoplasm  and  dependent  on 
metabohsm  may  be  superposed  on  these  simple  physical 
effects. 

An  important  difference  between  the  structure  of 
protoplasm  and  that  of  a  typical  artificial  emulsion, 
like  oil  in  water,  is  that  the  two  phases  separated  by  a 
protoplasmic  film  are  not  necessarily  aqueous  and  non- 
aqueous, respectively,  but  may  both  be  aqueous.  Any 
suspension  of  living  cells,  such  as  blood,  illustrates  this 
condition;  both  the  interior  of  the  corpuscle  and  the 
serum  are  complex  aqueous  solutions,  and  the  film 
bounding  the  corpuscle  is  too  thin  to  be  optically  detect- 
able as  a  separate  structure.  Yet  it  can  readily  be 
shown  by  osmotic  methods  that  a  semi-permeable 
membrane  is  there  present.  Similarly  within  the  limits 
of  a  single  cell  various  structurally  distinct  regions, 
sometimes  optically  distinguishable,  sometimes  not,  are 
to  be  regarded  as  separated  by  thin  films.  The  details 
of  this  film  structure  will  naturally  vary  in  different 
types  of  cell. 

The  surface  layer  of  the  entire  cell,  the  plasma 
membrane,  is  the  modified  surface-film  which  separates 
the  internal  protoplasm  from  its  surrounding  medium 
and  through  which  the  necessary  interchange  of  material 


I02  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

is  effected.  During  life  it  behaves  as  if  it  were  semi- 
permeable and  water-insoluble;  yet  it  is  evident  that 
it  allows  passage,  at  least  at  certain  times,  to  water 
and  many  dissolved  substances;  e.g.,  food-substances. 
Because  of  its  special  character  as  an  intermediary 
structure  or  organ,  its  properties  require  special  con- 
sideration in  any  study  of  the  properties  of  protoplasm. 
In  some  respects  the  properties  of  the  plasma 
membrane  appear  difficult  to  explain  on  known  physical 
grounds  or  even  paradoxical.  If  a  diffusible  food- 
substance  passes  through  the  membrane  into  the  cell  it 
may  there  undergo  metabolism,  but  it  is  difficult  to 
see  how  any  such  substance  can  enter  without  other 
important  substances  leaving.  If  simple  diffusion  alone 
is  the  chief  factor  in  the  entrance  and  exit  of  dissolved 
materials,  we  should  expect  that  any  increase  of  per- 
meability sufi&cient  to  allow  the  entrance  of  substances 
like  sugar  would  also  involve  a  loss  of  diffusible  cell 
constituents  to  the  exterior.  It  seems  necessary  to 
assume  that  the  conditions  determining  the  normal 
transport  of  substances  across  the  cell  boundary  are  of  a 
special  kind,  and  that  diffusion  is  only  one  of  a  number 
of  factors.  In  fact  we  know  that  in  secretion  and 
absorption  special  physiological  mechanisms  of  transport 
are  concerned,  by  which  water  and  dissolved  substances 
are  actively  conveyed  into  and  out  of  the  cell,  fre- 
quently against  concentration-gradients.  This  process 
requires  the  performance  of  work  by  the  cell,  just  as 
does  the  process  of  muscular  contraction,  although 
its  exact  conditions  are  at  present  unknown.  Many 
substances  (sugar,  salts,  amino-acids,  urea)  may  thus 
be  transported  from  regions  of  lower  to  regions  of  higher 


PROTOPLASMIC  STRUCTURE  103 

concentration,  a  process  necessarily  involving  osmotic 
work;  in  this  work  O2  is  consumed  and  energy  set  free. 
The  problem  of  the  nature  of  this  physiological  trans- 
porting mechanism  is  often  distinguished  as  the  problem 
of  ''physiological  permeabihty"  from  the  simpler  prob- 
lem of  the  conditions  of  simple  diffusion  across  the  cell 
surface,  or  "physical  permeabihty."  The  majority  of 
recent  studies  on  protoplasmic  permeability  have  had 
reference  to  this  latter  problem. 

It  will  be  apparent  that  the  problem  of  the  nature 
and  conditions  of  cell-permeability  is  not  a  special  or 
limited  one  but  underlies  the  whole  problem  of  the 
essential  nature  of  protoplasmic  structure  and  activities. 
Apparently  the  most  fundamental  property  of  the  plasma 
membrane  is  semi-permeability;  water  can  pass,  although 
with  considerable  resistance  in  many  cases;  but  the 
normal  water-soluble  constituents  of  the  protoplasm 
and  its  surroundings  do  not  diffuse  across  the  cell  bound- 
ary, or  only  under  special  conditions.  This  property 
of  ''semi -permeability"  is  associated  with  a  high  degree 
of  electrical  resistance  (signifying  impermeability  to 
crystahoidal  ions)  and  water-insolubility.  The  physico- 
chemical  conditions  of  these  properties  of  the  plasma 
membrane  have  been  much  investigated  of  recent  years, 
and  since  the  results  of  this  work  have  an  important 
bearing  on  our  general  problem,  a  somewhat  detailed 
review  will  be  given. 

The  general  importance  of  membranes  in  organic 
structure  and  activities  has  long  been  recognized,  and 
much  study  has  been  devoted  by  physiologists  to  various 
artificial  types  of  membrane,  such  as  precipitation 
membranes,   membranes   of  parchment   and   collodion, 


I04    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

and  various  impregnated  types  of  membrane,  in  the 
hope  of  throwing  Hght  upon  the  pecuHarities  of  living 
membranes.  The  resemblance  of  these  artificial  struc- 
tures with  the  protoplasmic  membranes  seems,  however, 
in  many  cases  remote.  The  conditions  observable  in 
living  protoplasm  indicate  that  membranes  of  a  different 
and  somewhat  special  type,  viz.,  the  interfacial  films 
formed  between  the  separate  phases  in  emulsions  and 
other  polyphasic  systems,  have  a  closer  affinity  with 
protoplasmic  membranes  than  any  other  simple  t>"pe  of 
physical  structure. 

The  property  of  forming  thin  films  at  structural  sur- 
faces of  all  kinds  is  highly  characteristic  of  living  proto- 
plasm. The  entire  cell  body  is  separated  from  the 
surrounding  medium  by  the  plasma  membrane;  within 
the  cell  the  nuclear  area  is  sharply  delimited  by  a  mem- 
brane which  usually  disappears  only  during  mitosis; 
structurally  distinct  membranes  are  also  formed  about 
fibrils,  vacuoles,  alveoli,  chromatophores,  spheres, 
chromosomes,  and  various  cell-inclusions.  Apparently 
the  conditions  required  for  the  formation  of  thin  solid 
films  are  present  everyw^here  in  living  protoplasm;  at 
any  structurally  well-defined  surface,  continuous  sheets 
of  material  may  be  deposited;  the  formation  of  mem- 
branes at  cut  surfaces  and  about  extruded  portions  of 
protoplasm  is  simply  one  illustration  of  this  general 
property.^  The  fertilized  eggs  of  marine  animals 
(sea-urchin,  starfish)  are  especially  favorable  objects 
for  showing  this  property;   new  films  are  rapidly  formed 

^  For  a  recent  account  of  these  phenomena,  see  the  review  by  Seifriz, 
Annals  of  Botany,  LXXXVIII  (1921),  269;  cf.  also  Botanical  Gazette, 
LXX  (1920),  360. 


PROTOPLASMIC  STRUCTURE  105 

at  the  surfaces  of  cuts  made  with  microdissection 
needles,  or  around  isolated  portions  of  protoplasm.' 

Apparently  the  nearest  inorganic  analogies  to  these 
protoplasmic  film-structures  are  the  thin  surface-films 
deposited  at  the  boundaries  between  mutually  insohible 
liquids,  one  or  other  of  which  contains  surface-active 
(especially  colloidal)  materials  in  solution;  good  illus- 
trations are  the  films  of  soap  or  other  material  surround- 
ing the  droplets  in  an  oil-water  or  other  emulsion,  or  the 
solid  films  formed  about  globules  of  oil,  mercury,  chloro- 
form, or  other  insoluble  liquids  immersed  in  protein- 
containing  solutions,  or  the  haptogen  membranes  formed 
at  the  surfaces  of  warm  soap  solution,  milk,  or  solutions 
of  protein,  peptone,  saponin  or  other  surface-active 
colloidal  substances.  Under  certain  conditions  these 
films  may  acquire  a  solid  consistency  and  exhibit  con- 
siderable structural  density,  and  thus  limit  diffusion 
between  the  two  phases;  the  resulting  system  may  then 
be  described  as  triphasic,  the  three  phases  being  the 
internal  medium,  the  external  medium,  and  the  inter- 
vening thin  phase  or  membrane.  The  ''artificial  cells" 
described  by  Harvey,''  made  by  breaking  up  a  chloroform 
solution  of  lecithin  in  dilute  egg-albumin,  may  be  cited 
as  examples  of  structures  formed  under  these  conditions. 

In  living  protoplasm  it  is  to  be  presumed  that 
condensation-films  of  protein  and  other  surface-active 
substances  are  formed  at  all  of  the  surfaces  bounding 

^  Chambers,  American  Journal  of  Physiology,  XLIII  (191 7),  i;  Pf^^- 
ceedings  of  the  Society  of  Experimental  Biology  and  Medicine,  XVII 
(1919),  41;  Jour.  Gen.  Physiol.,  V  (1922),  189.  For  plant  cells  cf. 
Prowazek,  Biol.  Zentr.,  XXVII  (1907),  737-  Drops  of  protojilasm 
from  Vaucheria  form  membranes  about  their  surfaces. 

2  E.  N.  Harvey,  Science,  XXXVI  (191 2),  564. 


io6    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

the  different  phases;  and  the  physical  resemblances 
between  protoplasm  and  emulsions  are  apparently 
referable  to  the  presence  of  these  surface-films.  Both 
systems  are  examples  of  what  may  be  called  film- 
pervaded  or  film-partitioned  systems.  By  the  formation 
of  these  films  a  certain  structure  is  imparted  to  the  whole 
system;  this  structure  is  largely  the  expression  of 
surface-forces,  in  which  chemical,  electrical,  and  mechan- 
ical (surface-tension)  factors  all  enter. 

It  should  be  noted  that  according  to  this  conception 
of  protoplasmic  structure  no  essential  distinction  is  to 
be  drawn  between  the  intracellular  surface-films  or 
membranes  (alveolar  membranes,  vacuole  membranes, 
nuclear  membranes)  and  the  surface-films  inclosing 
entire  cells  (plasma  membranes).  In  plant  cells  it  can 
be  shown  experimentally  that  vacuole  membranes  and 
plasma  membranes  are  similar  in  osmotic  properties, 
and  Hamburger  has  shown  the  same  for  the  nuclear 
membranes  and  plasma  membranes  of  animal  cells.^ 

In  forming  a  general  conception  of  the  physico- 
chemical  characteristics  of  protoplasmic  membranes, 
the  properties  of  colloidal  gels,  especially  in  their  relation 
to  diffusion-processes,  may  be  taken  as  a  starting-point. 
In  a  gel,  i.e.,  a  solid  mixture  of  colloidal  material  (such  as 
gelatine)  and  water,  diffusion  is  hindered  only  slightly  if 
the  concentration  of  the  colloid  is  low.  When  the  gel 
is  made  denser — as  the  proportion  of  water  is  decreased — 
diffusion  becomes  slower  and  more  restricted.  At  a 
sufficiently  high  density  certain  solutes,  especially 
colloids,  can  no  longer  diffuse  through  the  gel,  although 
water  and  crystalloids  may  still  pass.     If  the  density 

^  Hamburger,  Osmotischer  Druck  ii.  lonenlehre,  III,  8  ff. 


PROTOPLASMIC  STRUCTURE  107 

be  still  further  increased,  crystalloids  and  finally  even 
water  fail  to  pass.'  This  last  condition  is  exemplified 
in  water-proof  organic  membranes  like  the  external 
skin  of  most  animals  and  the  membranes  of  certain  eggs 
(the  Fundulus  egg).  From  an  elementary  or  purely 
physical  point  of  view  a  membrane  may  be  regarded  as 
essentially  a  thin  sheet  consisting  of  a  gel  of  the  kind 
above.  Such  a  gel  has  a  large  surface-area  in  proportion 
to  its  total  volume,  and  by  virtue  of  its  diffusion-hindering 
property  it  prevents  or  retards  the  transfer  of  material 
(colloidal  particles,  molecules,  ions)  between  the  two 
solutions  which  it  separates. 

Connected  with  this  diffusion-hindering  property, 
which  conditions  the  rate  of  interchange  and  hence  the 
rate  of  chemical  activity  at  the  surface  between  the 
solutions  separated,  are  certain  electrical  properties 
(*' membrane-potentials"),  resulting  from  the  influence 
of  the  membrane  on  the  distribution  and  transfer  of 
ions  between  the  two  solutions.^  These  properties  are 
apparently  of  fundamental  importance  to  the  bioelectric 
processes,  and  their  conditions  will  be  considered  more 
fully  later. 

Independently  of  its  structural  density,  a  membrane 
of  complex  chemical  composition  may  exhibit  a  selective 

^  Tlie  conditions  may  be  compared  with  those  presented  by  a  series 
of  "ultra-filters"  of  graded  densities,  as  described  by  Bechhold  {Colloids 
in  Biology  and  Medicine);  the  permeability  decreases  as  the  density 
increases. 

^Cf.  Lewis,  A  System  of  Physical  Chemistry,  II  (1920),  320,  for  an 
account  of  membrane  potentials.  The  type  of  equilibrium  investigated 
by  Donnan,  in  which  solutions  are  separated  by  a  membrane  which  is 
impermeable  to  some  but  not  all  of  the  ions,  plays  an  important  part  in 
many  membrane  processes,  as  shown  especially  by  Loeb  in  his  recent 
work.     Cf.  Proteins  and  the  Theory  of  Colloidal  Behavior,  Part  2. 


io8    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

permeability  with  reference  to  substances  which  are 
unequally  soluble  in  its  different  chemical  components. 
Substances  soluble  in  a  given  component  (lipoid-soluble 
substances)  may  thus  pass  a  protoplasmic  membrane, 
while  chemically  similar  but  lipoid-insoluble  substances 
may  not.  Overton's  experiments  on  the  differences 
between  the  rates  of  diffusion  of  various  organic  com- 
pounds and  salts  into  living  cells  illustrate  selective 
permeability  of  this  type.' 

It  is  important  to  recognize  that  the  plasma  mem- 
brane is  not  a  dead  structure  or  a  purely  passive  partition, 
but  represents  in  reality  a  portion  of  the  living  proto- 
plasm, characteristically  modified  in  its  structure  and 
physical  properties  by  surface  conditions.^  Hence  it 
is  the  seat  of  metabolic  and  other  activities  which  influ- 
ence its  physical  properties.  Evidently  it  is  that  part 
of  the  cell  which  comes  into  the  most  direct  relations 
with  the  surroundings.  Hence  many  changes  in  the 
surroundings  influence  the  cell  primarily  through  their 
action  on  the  plasma  membrane,  and  there  is  evidence 
that  in  irritable  cells  this  structure  plays  the  part  of  a 
specially  sensitive  and  reactive  intermediary  between 
the  living  protoplasm  and  the  external  world;  it  thus 
exerts  a  far-reaching  control  over  the  metabolic  and  other 
processes  occurring  in  the  cell-interior.  The  relations  of 
the  plasma  membrane  to  stimulation  will  be  considered 
in  detail  later. 

^  Cf.  Overton's  summary  of  his  work  in  Nagel's  Handhuch  der 
Physiologie,  II  (1907),  744. 

^  Cf.  my  paper  in  American  Journal  of  Physiology,  XLV  (1918),  406, 
for  a  more  complete  discussion  of  this  phase  of  the  problem  of  perme- 
ability. 


PROTOPLASMIC  STRUCTURE  109 

The  normal  semi-permeability  of  the  plasma  mem- 
brane is  a  function  of  the  living  state  of  the  cell,  i.e.,  is 
dependent  upon  the  continuance  of  the  normal  construc- 
tive metabolism.  When  metabolism  ceases,  as  at  death, 
the  membrane  soon  loses  its  insulating  or  semi-permeable 
properties,  and  free  interchange  of  diffusible  substances 
then  occurs  between  the  cell  and  the  medium.  The  loss 
of  turgor  in  plant  cells  after  death  is  the  most  familiar 
example  of  this  type  of  effect;  leaves  and  other  paren- 
chymatous parts  then  wilt  because  of  the  diffusion  of  the 
osmotically  active  substances  through  the  now  permeable 
plasma  membranes.  The  osmotic  tension  which  during 
life  keeps  the  cell  walls  in  their  normal  stretched  and  rigid 
condition  disappears,  the  tissue  becomes  soft  and  flaccid, 
and  the  protoplasm  shows  other  evidences  of  increased 
permeability  (increased  electrical  conductivity,  loss  of 
diffusible  materials  to  the  surroundings,  ready  entrance 
of  dyes  and  other  substances).  Similarly  in  animal  cells 
various  substances,  such  as  pigments  and  other  com- 
pounds, normally  confined  within  the  protoplasm, 
diffuse  rapidly  into  the  surrounding  medium  on  death, 
and  the  plasma  membrane  admits  substances  such  as 
alkahs  and  salts,  to  which  previously  it  was  impermeable. 

It  is  a  remarkable  and  apparently  paradoxical  fact 
that  the  living  plasma  membranes  usually  show  them- 
selves highly  impermeable  to  many  dissolved  substances 
which  are  essential  to  the  cell  as  foods  or  otherwise 
(sugars,  amino-acids,  and  neutral  salts),  and  some 
general  explanation  of  this  peculiarity  seems  required. 
If  we  were  to  express  the  matter  teleologically  we  might 
say  that  the  advantage  to  the  cell  consists  in  the  insula- 
tion  of   the   living  protoplasm   from   its   environment, 


no  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

which  has  an  entirely  different  composition.  The 
maintenance  of  the  normal  vital  properties  requires  that 
the  essential  diffusible  constituents  of  protoplasm  should 
not  be  lost  to  the  surroundings;  it  is  also  evident  that 
too  ready  an  entrance  of  substances  from  the  outside 
would  interfere  with  the  stability  of  protoplasmic 
composition.  The  presence  of  a  semi-permeable  bound- 
ary layer  appears  thus  to  be  a  necessary  condition  for  the 
preservation  of  the  normal  chemical  organization  of  the 
cell.  It  is  readily  seen,  for  example,  that  the  existence  of 
a  simple  diffusion  equilibrium  between  surrounding 
medium  and  protoplasm  would  prevent  the  latter 
from  acquiring  the  special  crystalloidal  content  which  is 
characteristic  of  it.  Hence,  living  cells  are  enabled  to 
survive  and  develop  largely  by  virtue  of  being  inclosed 
by  surface-films  which  are  impermeable  to  crystalloidal 
compounds  of  the  foregoing  classes. 

But  since  these  compounds  do  in  fact  gain  entrance 
to  the  cell,  at  least  at  certain  times,  it  is  clear  that  the 
problem  of  cell-permeability  is  not  a  simple  one.  Appar- 
ently we  must  conclude  that  the  entrance  or  exit  of 
substances  by  simple  diffusion  is  in  most  cases  a  different 
phenomenon  from  their  entrance  or  exit  under  physio- 
logical conditions.  The  processes  of  absorption  and 
secretion  are  in  fact  special  activities,  requiring  the 
performance  of  work  by  the  cell.  The  distinction 
between  a  passive  or  purely  physical  permeability  and 
an  active  or  physiological  permeability  thus  ^  seems  a 
necessary  one. 

The  conditions  of  passive  permeability  are  of  interest 
chiefly  because  of  the  light  which  they  throw  upon  the 
physical  and  chemical  nature  of  the  substances  composing 


PROTOPLASMIC  STRUCTURE  m 

the  plasma  membranes.  The  most  significant  general 
fact  is  that  apparently  all  substances  with  solubilities 
or  solvent  properties  characteristic  of  organic  compounds 
(rather  than  of  water-soluble  compounds  or  water)  enter 
cells  with  special  readiness.  A  relation  between  the 
presence  of  organic  solvents  in  protoplasm  and  the 
permeabihty  of  the  plasma  membrane  is  thus  indicated. 
Overton,  who  first  investigated  in  detail  this  connection 
between  organic  solubility  and  power  of  penetration, 
drew  the  conclusion  that  the  plasma  membrane  consisted 
essentially  of  the  so-called  "lipoid"  compounds,  espe- 
cially lecithin  and  cholesterol,  which  are  universally 
present  in  protoplasm.  He  showed  that  all  members  of 
homologous  series,  such  as  alcohols,  ethers,  esters,  normal 
and  substituted  hydrocarbons,  ketones,  aldehydes, 
amides,  and  similar  compounds,  readily  enter  living 
cells;  such  compounds  dissolve,  or  are  dissolved  by,  the 
lipoids  or  solutions  of  lipoids  in  organic  solvents;  and 
their  ready  entrance  is  a  result  of  this  solubility.  On 
the  other  hand,  sugars  and  polyatomic  alcohols  (pentites, 
hexites,  etc.),  with  molecules  containing  many  h}'droxyl 
groups,  are  highly  soluble  in  water,  but  not  in  lipoids, 
and  do  not  enter  cells  readily.  In  Overton's  original 
experiments,  acid  and  basic  dyes  also  showed  a  relation 
between  lipoid-solubiKty  and  power  of  penetration;  but 
the  conditions  are  complex  in  this  case  and  many  excep- 
tions to  this  rule  are  now  known.'  In  the  case  of  neutral 
salts  of  alkali  and  alkah  earth  metals  (especially  Xa, 
K,  and  Ca)  there  is  also  httle  or  no  evidence  of  penetra- 

^Cf.  Ruhland,  Jahrh.  wiss.  Botanik,  XLVI  (190S),  i;  cf.  also 
Hober's  discussion,  Physikalische  Chemie  der  Zelle  und  dcr  Gcwcbe, 
pp.  426  £f. 


112    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

tion  in  balanced  solutions,  a  fact  corresponding  to  the 
lipoid-insolubility  of  these  compounds.  In  pure  solutions 
(pure  NaCl  solution)  the  salts  alter  the  properties  of  the 
plasma  membranes  and  secondarily  may  penetrate;^ 
but  this  fact  is  in  no  way  inconsistent  with  Overton's 
view,  which  applies  to  the  unaltered  membrane.  A 
definite  correlation  between  lipoid-solubility  and  power 
of  penetrating  the  living  plasma  membrane  may  be 
said  to  have  been  established  by  Overton's  work  and 
succeeding  studies  of  the  same  kind;  and  this  generaliza- 
tion is  an  important  one,  since  it  indicates  (as  do  many 
other  facts)  that  the  lipoids  play  an  essential  part, 
apparently  in  association  with  the  other  chief  colloidal 
compounds  of  protoplasm,  the  proteins,  in  the  formation 
of  membranes  and  probably  of  the  other  solid  structural 
elements  of  cells. 

Three  chief  methods  have  been  employed  in  determin- 
ing the  permeability  of  cells  to  dissolved  substances: 
(i)  the  plasmolytic  or  osmotic  method,^  (2)  the  partition 
method,^  and  (3)  the  electrical  conductivity  method. "^ 
To  these  may  be  added  methods  dependent  on  the  use 
of  indicators,   either   those  normally  present  in  cells,^ 

^  Cf.  Osterhout,  Science,  XXXIV  (1911),  187. 

2  Overton,  Arch.  ges.  Physiol.,  XCII  (1902),  115. 

3  Hedin,  Arch.  ges.  Physiol.,  LXVIII  (1897),  229. 

4Tangl  and  Bugarszky,  Zentr.  Physiol.,  XI  (1897),  297;  G.  N. 
Stewart,  ibid.,  p.  332;  Osterhout,  Science,  XXXV  (1912),  112,  and 
later  papers;  also  Osterhout's  recent  book,  Injury,  Recovery  and  Death 
in  Relation  to  Conductivity  and  Permeability,  Philadelphia,  1922. 

s  Harvey,  Internal.  Z.  physik.-chem.  Biol.,  I  (1914),  463;  Crozier, 
Journal  of  Biological  Chemistry,  XXIV  (1916),  255,  and  Jour.  Gen. 
Physiol.,  IV  (1922),  723;  Haas,  Journal  of  Biological  Chemistry,  XXVII 
(1916),  225.  Cf.  also  Jacobs,  American  Journal  of  Physiology,  LIII 
(1920),  457. 


PROTOPLASMIC  STRUCTURE  113 

or  dyes  like  neutral  red'  which  may  be  introduced  from 
outside.  These  methods  are  especially  valuable  in 
studying  the  permeability  to  acids  or  alkalis.  Per- 
meabihty  to  dyes  may  usually  be  studied  by  direct 
observation. 

The  method  of  plasmolysis,  first  employed  systemati- 
cally by  Overton,  is  based  on  the  production  of  osmotic 
effects  (entrance  or  exit  of  water)  when  the  cell  is  placed 
in  solutions  having  a  different  osmotic  pressure  from 
that  of  the  cell-contents  (anisotonic  solutions).  In 
hypertonic  solutions  of  substances  which  do  not  readily 
traverse  the  plasma  membrane  the  cell  shrinks,  in 
hypotonic  solutions  it  swells,  while  in  isotonic  solutions 
its  volume  remains  unchanged.  The  problem  is  to 
determine  the  relative  degree  of  permeability  to  differ- 
ent substances,  some  of  which  may  traverse  the  mem- 
brane, but  with  unequal  readiness.  To  do  this  the 
behavior  of  the  cell  is  observed  in  a  hypertonic  solution 
of  the  substance  under  examination.  It  is  clear  that 
when  the  dissolved  substance  in  the  external  medium 
is  quite  unable  to  penetrate  the  membrane,  it  exerts 
pressure  against  the  latter  (by  the  continued  impacts 
of  the  molecules),  and  since  this  pressure  is  greater  than 
that  exerted  by  the  dissolved  molecules  within  the  cell, 
water  is  extracted  (or  expressed)  from  the  latter  until  a 
permanent  state  of  equilibrium  is  reached  in  which  the 
osmotic  pressure  of  the  cell-contents  equals  that  of  the 
surrounding  solution.  The  cell  is  then  permanently 
shrunken.     When,    however,    the    dissolved    substance 

^Bethe,  Arch.  ges.  Physiol.,  CXXVII  (1909),  219;  Warburg, 
Z.  physiol.  Chem.,  LXVI  (1910),  305;  Harvey,  Journal  of  Experimental 
Zoology,  X  (191 1),  507;    Chambers,  Jour.  Gen.  Physiol.,  V  (1922),  189. 


114   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

penetrates  gradually,  its  water-abstracting  effect  is  only 
temporary,  since  its  concentration,  at  first  greater 
outside  than  inside  the  cell,  is  eventually  equalized  by 
diffusion;  the  cell  then  tends  to  resume  its  original 
water-content.  In  the  case  of  a  solute  which  penetrates 
rapidly  (with  a  readiness  like  that  of  water)  no  effective 
inwardly  directed  pressure  can  be  exerted  against  the 
membrane  and  no  osmotic  eft'ect  is  produced. 

Using  plant  cells  (Spirogyra  and  others)  and  moder- 
ately hypertonic  solutions  of  various  substances,  Overton 
found  that  in  solutions  of  sugars,  amino-acids,  and  neutral 
salts  the  plasmolysis  was  permanent;  in  solutions  of 
glycerine,  glycol,  urea,  and  similar  compounds  the 
degree  of  plasmolysis  was  less  than  in  sugar  solutions, 
and  after  the  initial  shrinkage,  water  gradually  re- 
entered the  cell;  while  in  solutions  of  alcohols  and  many 
other  organic  substances  (of  the  same  osmotic  pressure 
as  the  effective  sugar  solutions)  plasmolysis  was  entirely 
absent.  Similar  differences  were  typical  of  a  large 
number  of  other  compounds.  He  therefore  divided 
soluble  substances  into  three  groups,  according  to  their 
ability  to  penetrate  the  living  plasma  membrane: 
(i)  Those  to  which  the  plasma  membrane  is  completely 
or  nearly  impermeable,  including  sugars,  polyatomic 
alcohols  (from  erythrite  up),  soluble  amino-acids,  neutral 
salts  of  alkali  and  alkali  earth  metals;  (2)  those  which 
penetrate  the  membrane,  but  slowly  and  with  varying 
degrees  of  resistance,  including  glycol,  glycerol,  and 
certain  amides  such  as  urea;  and  (3)  those  which  enter 
without  encountering  any  evident  resistance;  here 
belong  a  variety  of  organic  compounds  of  the  groups 
cited  above.     These  general  conditions  were  found  by 


PROTOPLASMIC  STRUCTURE 


"5 


Overton  and  other  investigators  to  be  characteristic 
both  of  animal  cells  (blood  corpuscles,  muscle  cells, 
egg  cells,  etc.)  and  plant  cells  of  the  most  varied  kinds. 

In  the  partition  method,  as  used  by  Hedin  and  others, 
the  distribution  of  dissolved  substances  between  the 
cells  and  the  solution  is  measured  directly  (by  cryoscopic 
determinations),  and  its  results  agree  closely  with  those 
of  the  plasmolytic  method.  In  general  it  has  been  found 
that  the  above-cited  conditions  of  permeability  are  highly 
characteristic  if  not  universal  in  living  protoplasm.' 

Since  in  general  the  lipoid-soluble  substances  which 
penetrate  living  protoplasm  are  also  highly  surface- 
active,  the  conclusion  may  be  drawn  that  either  lipoid- 
solubility  or  surface-activity  (or  both)  is  a  property 
favorable  to  penetration  (Overton,  Traube).  The 
penetration  of  one  substance  through  another  may 
depend  on  mutual  solubility;  the  cases  of  the  rubber 
membranes  used  in  Flusin's  experiments,  the  water- 
soaked  bladder  partitions  employed  by  Nernst,  and  the 
palladium  partitions  of  Ramsay's  experiments  with 
nitrogen  and  hydrogen  may  be  cited  as  illustrations.* 
Overton  explains  the  permeability  of  the  plasma  mem- 
brane to  lipoid-soluble  substances  as  an  expression  of  the 
solubility  of  these  substances  in  the  lipoids  of  the  mem- 
brane; in  general  he  finds  a  paralleHsm  between  the 
lipoid-water  partition-ratio  of  a  given  substance  and 
its  abihty  to  penetrate  cells;  this  is  illustrated  by  the 
behavior  of  substitution-products  and  of  the  members  of 

^  Cf.  Hamburger's  Osmotischer  Druck  u.  lonenlehre  for  an  account 
of  comparative  investigations  in  this  field. 

^'Flusin,  Ann.  de  chim.  et  phys.,  XIII  (1908),  4S0;  Xcrnst,  Z. 
physik.  Chem.,  VI  (1890),  37;  Ramsay,  Z.  physik.  Chcm.,  XV  (1894), 
518.     Cf.  p.  144  below. 


ii6    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

homologous  series.  The  contrast  between  NH4OH 
(lipoid-soluble)  and  KOH  (lipoid-insoluble)  in  their 
ability  to  enter  living  cells  is  a  striking  one;^  and  most 
investigators  who  have  studied  the  penetration  of  sub- 
stances (like  acids  and  bases)  whose  behavior  can  be 
determined  with  accuracy,  have  found  a  general  parallel- 
ism between  the  rate  of  penetration  and  the  lipoid- 
solubility  of  the  various  compounds.  This  parallelism, 
however,  is  not  exact,  indicating  the  presence  of  other 
factors.^ 

Impermeability  to  neutral  salts  in  balanced  solution 
is  an  especially  important  property  of  the  plasma  mem- 
brane, since  it  renders  possible  permanent  differences 
of  salt-content  between  protoplasm  and  surroundings. 
This  means  differences  of  ionic  content,  and  is  probably 
a  condition  of  the  normal  electrical  polarization  ("physio- 
logical polarization")  of  the  membrane,  since  any 
partition  separating  two  solutions  of  different  ion-content 
is  typically  the  seat  of  an  electrical  potential  difference. 
The  results  of  the  mineral  analysis  of  cells,  as  well  as 
those  of  the  plasmolytic  and  partition  methods  just 
described,  show  clearly  the  inability  of  neutral  salts  to 

^  Cf.  Warburg,  loc.  cit.;  Harvey,  loc.  cit.;  Gray,  Proceedings  of  the 
Royal  Society,  B,  XCIII  (1922),  104  (cf.  p.  no);  Jacobs,  Jour.  Gen. 
Physiol.,  V  (1922),  181.  A  similar  contrast  exists  between  organic 
acids  (lipoid-soluble)  and  strong  acids;  cf.  Loeb,  Biochem.  Zeitschrift, 
XV  (1909),  254;  Bethe,  loc.  cit.;  Gray,  loc.  cit.  Jacobs' results  especially 
show  the  extraordinary  ease  with  which  carbon  dioxide  and  ammonia 
penetrate  living  protoplasm. 

2  Harvey,  Intern.  Z.  physik.  chem.  Biol.,  I  (1914),  463;  Crozier, 
loc.  cit.  Miss  CoUett's  studies  on  the  toxicity  of  acids  to  infusoria  show 
a  similar  general  relationship  between  organic  solubility  and  toxicity 
{Journal  Experimental  Zoology,  XXIX  [1919],  443,  and  XXXIV  [1921], 
67,  75)- 


PROTOPLASMIC  STRUCTURE 


117 


penetrate  the  unaltered  living  cell.  Paine'  has  shown 
experimentally  that  NaCl,  (NH4),S04,  and  Xa^HPO^ 
in  n/io  solution  do  not  enter  yeast  cells  appreciably 
even  after  hours  of  immersion;  and  numerous  analyses 
have  shown  that  the  specific  salt-content  of  many 
living  cells  (blood  corpuscles,  muscle,  etc.)  is  quantita- 
tively or  even  qualitatively  entirely  different  from  that 
of  the  medium.  For  example,  sodium  salts  seem  to  be 
almost  completely  absent  from  vertebrate  muscle  cells. ^ 
This  result  seems  incompatible  with  more  than  a  very 
limited  permeability  of  the  plasma  membrane  to  these 
substances.  Either  the  salts  do  not  diffuse  across  the 
membrane,  or  some  active  physiological  factor  is  at 
work  which  opposes  or  compensates  the  effect  of  diffusion 
and  maintains  the  salt  content  of  the  protoplasm  at  a 
certain  norm.  The  nature  and  proportion  of  the  salts 
present  in  any  species  of  cell  are  characteristic  of  that 
cell  and  apparently  represent  a  constant  feature  of  its 
chemical  organization;  this  is  illustrated,  for  example,  in 
the  analyses  of  the  salt-content  of  mammalian  blood 
corpuscles  by  Abderhalden  and  others.^  In  the  cor- 
puscles of  the  horse,  pig,  and  rabbit  there  is  Httle  or 
no  Na  and  an  abundance  of  K;  in  the  ox,  sheep,  goat, 
dog,  cat,  the  amount  of  Na  is  greater  than  that  of  K. 
Inorganic  phosphates  are  always  much  more  concen- 
trated in  the  corpuscles  than  in  the  serum,  which  is 
always  rich  in  Na  and  poor  in  K.  \'oluntar\'  muscle 
cells  are  rich  in  K  salts  and  phosphates  and  poor  in 
Na  salts. 

^  Paine,  Proceedings  of  the  Royal  Society,  B,  LXXXIV  (1912),  2S9. 

2  Urano  and  Fahr,  cf.  chap.  viii. 

3  Hober,  loc.  cit.,  p.  370. 


ii8    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

Hober  {op.  cit.,  p.  371)  cites  certain  observations  of 
Warburg  made  in  1911^  indicating  that  the  erythrocytes 
of  the  goose  are  influenced  in  their  oxygen- consumption 
by  alkah-earth  salts  only  after  the  plasma  membrane 
has  been  destroyed  by  freezing  and  thawing.  Apparently 
these  salts  cannot  pass  the  intact  plasma  membrane. 
On  the  other  hand,  alcohols  and  urethanes  check  oxida- 
tions in  the  intact  erythrocytes;  these  substances  can 
penetrate.  It  may  be  noted  that  these  observations 
are  consistent  with  the  view  that  the  nuclear  surface 
is  a  chief  factor  in  the  oxidation-processes  of  these  cells.^ 

The  relative  or  complete  impermeability  of  blood 
corpuscles  to  the  ions  of  the  surrounding  salt  solution  is 
also  indicated  by  the  low  electrical  conductivity  of 
these  cells.  Stewart,  Tangl,,  Bugarszky,  and  others 
have  shown  that  the  electrical  conductivity  of  blood  is 
due  almost  entirely  to  the  plasma.  Low  electrical 
conductivity  is  in  fact  now  known  to  be  a  highly  constant 
and  characteristic  peculiarity  of  cells  during  life,  and 
the  evidence  indicates  that  the  high  resistance  is  chiefly 
if  not  entirely  a  property  of  the  plasma  membranes. 
The  conductivity  of  the  cell  as  a  whole  appears  to  vary 
directly  with  the  permeability  of  the  plasma  membrane 
to  crystalloidal  solutions.  All  conditions  that  increase 
general  permeability  (action  of  cytolytic  substances  or 
unbalanced  salt  solutions  or  of  poisons,  high  tempera- 
tures, or  other  lethal  agents)  also  increase  electrical 
conductivity.     According  to  Osterhout,  the  most  exact 

^Warburg,  Z.  physiol.  Chem.,  LXX  (191 1),  413- 

2  In  the  nucleated  erythrocytes  of  the  frog,  the  indophenol  test 
shows  active  oxidation  at  the  nuclear  surface;  cf.  R.  S.  Lillie,  Journal  of 
Biological  Chemistry,  XV  (1913),  237. 


PROTOPLASMIC  STRUCTURE  119 

measurements  of  permeability  are  those  given  Ijy  elec- 
trical conductivity.  The  conductivity  of  a  living  tissue 
is  a  measure  of  its  permeability  to  ions;  and  while  it  is 
conceivable  that  the  permeability  to  other  substances, 
such  as  non-electrolytes  like  sugar,  may  vary  inde- 
pendently (within  certain  limits)  of  the  permeability  to 
ions,  the  advantages  of  estimating  permeability  quan- 
titatively are  such  that  the  conductivity  method  must 
be  regarded  as  the  one  to  be  preferred  wherever  it  can 
be  applied. 

Osterhout  has  shown  that  by  means  of  the  con- 
ductivity method  the  permeability  of  plant  tissues 
under  varying  external  conditions  can  be  readily  and 
accurately  determined;  also  that  permeability  can  be 
varied  at  will,  reversibly,  in  either  direction,  especially 
under  the  influence  of  neutral  salts  and  lipoid-solvent 
compounds/  In  pure  NaCl  solutions  the  permeability 
of  Laminaria  fronds  is  increased,  to  a  degree  depending 
on  the  duration  of  exposure  and  the  temperature;  on 
replacing  the  tissue  in  sea  water  the  permeability  returns 
to  or  toward  the  normal,  the  degree  of  possible  recover^' 
depending  upon  the  extent  of  the  change  produced  by 
the  NaCl  solution."  If  the  permeability  has  been 
increased  beyond  a  certain  limit,  its  reversal  is  impossible 
and  the  plant  is  dead.  He  has  suggested,  therefore, 
that  the  property  of  ''vitality"  may  be  measured  by 
determining  the  electrical  resistance.^  Isotonic  CaCU 
solutions  have  the  opposite  kind  of  effect  and  at  first 
decrease  permeability;    the  antagonism  between  Na  and 

'  Osterhout,  loc.  cit.,  and  Science,  XXXVII  (1912),  3;  also  "Quanti- 
tative Researches  in  Permeability,"  The  Plant  World,  XVI  (1913).  i-'Q- 

2  Osterhout,  Jour.  Gen.  Physiol.,  Ill  (1920),  145. 

3  Osterhout,  Science,  XL  (1914),  488. 


I20   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

Ca  salts  is  thus  explained;  when  the  two  salts  are 
present  in  appropriate  proportions  (20  NaCl+i  CaClz) 
conductivity  is  unaltered,  and  the  tissue  remains  living 
for  days,  while  in  the  pure  solution  of  either  salt  toxic 
action  and  death  soon  result.  The  changes  of  perrnea- 
bility  accompanying  normal  physiological  processes  have 
also  been  measured  by  the  conductivity  method  in  cer- 
tain cases,  especially  by  McClendon  and  Gray  in  the 
fertilization  of  sea-urchin  eggs/ 

The  question  of  the  condition  of  the  salts  in  the  living 
protoplasm  arises  here;  and  this  question  is  of  consider- 
able general  importance,  since  it  has  been  held  by  certain 
investigators  that  these  salts  are  present  chiefly  or 
entirely  in  a  combined  or  adsorbed  state  and  are  hence 
not  free  to  act  as  conductors.  As  we  shall  see  later  in 
dealing  with  the  phenomena  of  stimulation  and  trans- 
mission, the  electrical  conductivity  of  the  internal 
protoplasm  appears  to  be  a  necessary  factor  in  its 
normal  activity;  and  any  evidence  that  this  conductivity 
is  what  we  should  expect  it  to  be  from  the  known  salt- 
content  of  protoplasm  is  of  interest.  The  contention 
that  the  salts  in  protoplasm  are  non-ionized,  or  that  the 
ions  are  in  some  manner  rendered  immobile,  is  incon- 
sistent with  the  physico-chemical  observations  relating 
to  the  behavior  of  salts  in  the  presence  of  proteins,  lipoids, 
or  other  colloids.  According  to  Bugarszky  and  Lieber- 
mann,  the  addition  of  even  large  quantities  of  protein 
to  salt  solutions  affects  the  ionic  concentration  only 
slightly;^    Michaelis  and  Rona^  have  shown  by  ''com- 

^  McClendon,  American  Journal  of  Physiology,  XXVII  (1910),  240J 
J.  Gray,  Journal  of  the  Marine  Biological  Association,  X  (1913),  50. 

^  Bugarszky  and  Liebermann,  Arch.  ges.  Physiol.,  LXXII  (1898),  51. 
3  Michaelis  and  Rona,  Biochem.  Zeitschrift,  XIV  (1908),  476. 


PROTOPLASMIC  STRUCTURE  121 

pensation  dialysis"  that  the  salts  in  serum  (containing 
10  per  cent  protein)  are  freely  dialyzable.  Pauli  and 
Samec  have  also  shown  that  alkali  salts  are  not  more 
soluble  in  serum  than  in  water.^ 

There  is  the  possibility  of  the  formation  of  com- 
binations with  the  amino-acids  present  in  the  proteins; 
but  the  salts  of  such  weak  acids  would  theoretically  be 
almost  completely  hydrolyzed;  i.e.,  a  stable  combination 
with  protein  in  which  the  salt  is  completeh-  and  firmly 
bound  is  scarcely  conceivable.  Any  protein-salt  com- 
binations thus  formed  would  hydrolyze,  and  the  products 
of  hydrolysis  would  diffuse  out  through  the  membrane  if 
the  latter  were  permeable;  and  further  hydrolysis  would 
proceed  until  an  equilibrium  was  reached  in  which  a 
large  proportion  of  salt  was  present  in  the  free  dissolved 
state.^ 

General  chemical  theory  thus  indicates  that  only  a 
very  small  proportion  of  the  salt  in  the  cell  can  be  in  a 
state  of  permanent  combination  with  protein;  hence  the 
characteristic  difference  between  the  salt-content  of  the 
cells  and  that  of  the  medium  cannot  be  thus  explained. 
It  is  probable,  therefore,  that  the  semi-permeability  of 
the  plasma  membrane  is  an  essential  factor  in  making 
possible  this  difference. 

If  it  were  possible  to  measure  the  electrical  con- 
ductivity of  the  cell  interior  apart  from  that  of  the 
plasma  membrane,  the  question  could  be  answered  at 
once.     According  to  the  view  presented  above,  the  chief 

'  Pauli  and  Samec,  Biochem.  Zeiischrifi,  XVII  (1909),  235. 

^  In  other  words,  the  proteins  and  other  compounds  present  in  the 
cell  could  not  hold  more  than  a  very  small  proportion  of  the  salts  in  a 
combined  and  indiffusible  form. 


122    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 


r~i 


■"g" 


sismsmU 


barrier  to  the  movement  of  ions  is  at  the  semi-permeable 
plasma  membrane.  The  increased  conductivity  observed 
at  death,  or  after  cytolysis  by  saponin  or  other  com- 
pounds, favors  this  view,  since  semi-permeability  is  then 
lost;  i.e.,  there  is  a  general  parallelism  between  the  ability 
of  salts,  sugars,  and  other  soluble  compounds  to  pass 
the  plasma  membranes  and  the  electrical  conductivity 

— a  fact  indicating  that  the 
chief  condition  rendering 
living  cells  such  poor  con- 
ductors of  electricity  is 
the  impermeability  of  the 
membranes  to  ions.  From 
these  considerations  we 
should  conclude  that  the 
ions  within  the  cell  are  free 
to  diffuse  within  the  space 
inclosed  by  the  plasma 
membrane.  But  the  case 
requires  to  be  tested  by 
experiment,  for  it  might 
be  held,  in  spite  of  the  fore- 
going considerations,  that 
the  electrolytes  are  in  some 
manner  chemically  combined  in  living  protoplasm  and 
are  set  free  only  at  death. 

Hober  has  attempted  to  measure  the  conductivity  of 
the  cell  interior,  using  in  part  methods  suggested  to  him 
by  Nernst.  A  device  of  the  plan  shown  in  Fig.  i  was  first 
employed.^  A  rapidly  alternating  current  is  induced 
in  the  circuit  containing  the  two  balanced  condensers 
^  Hober,  Arch.  ges.  Physiol.,  CXXXIII  (1910),  237. 


Fig.  I. — 7,  inductorium;  C,  condenser; 
G,  spark -gap;  S,  coil  (self-induction)  of  pri- 
mary circuit;  53,  coil  of  secondary  circuit ;  A, 
adjustable  condenser;  B,  condenser  with 
space  between  plates  for  insertion  of  vessel 
(F)  containing  suspension  of  cells;  D,  detec- 
tor in  bridge^  Ri,  Ri,  resistances  (from  Hober, 
loc.  cit.). 


PROTOPLASMIC  STRUCTURE        123 

A  and  B.  When  the  capacities  of  the  condensers  are 
the  same  and  the  resistances  of  the  two  halves  of  the 
circuit  (on  either  side  of  the  bridge)  are  the  same  (or 

when  their  ratios  are  equal;    i.e.,  when  ~  =  -^^]     no 

current  passes  through  the  detector;  but  if  the  capacity 
of  one  condenser  (A)  is  changed,  the  current  passes  until 
the  capacity  of  the  other  (B)  is  made  the  same.  Now 
the  capacity  of  a  condenser  is  increased  if  a  conducting 
layer  is  introduced  into  the  dielectric  between  the 
plates,  and  to  a  degree  which  is  proportional  to  the  con- 
ductivity of  the  layer.  Hober's  method,  therefore, 
consists  in  introducing  between  the  plates  of  one  of  the 
condensers  (B),  after  the  system  has  been  brought  into  a 
balanced  condition,  a  glass  vessel  containing  a  suspension 
of  living  cells  (blood  corpuscles)  in  isotonic  sugar  solution. 
Such  a  suspension  does  not  conduct  electricity  (in  the 
usual  Kohlrausch  sense),  yet  it  increases  the  capacity 
of  the  condenser  and  so  allows  a  current  to  flow  across 
the  bridge.  This  result  shows  that  the  suspension  con- 
tains an  electrically  conducting  fluid;  this  can  only  .be 
in  the  interior  of  the  cell,  since  the  suspension-medium 
is  sugar  solution,  which  is  a  non-conductor.  The 
addition  of  saponin  (which  destroys  the  membrane  and 
increases  the  Kohlrausch  conductivity)  was  found  not 
to  change  the  capacity,  indicating  that  the  conductivity 
of  the  cell-contents  is  the  same  whether  the  semi- 
permeable membrane  is  present  or  not.  If  a  glass  vessel 
containing  a  salt  solution  is  placed  between  the  condenser 
plates,  a  similar  increase  of  capacity  is  shown;  and  by 
comparing  the  effects  produced  by  salt  solutions  of 
known  conductivity  with  those  produced  by  suspensions 


124   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

of  cells,  the  internal  conductivity  of  the  latter  can  be 
estimated.  The  measurements  cannot  be  made  very 
exact;  they  indicate,  however,  that  the  internal  con- 
ductivity of  the  corpuscle  is  of  the  order  of  that  of  a  o.i  n 
KCl  solution  (between  o.i  n  and  o.oi  n). 

Hober  also  experimented  with  another  method  some- 
what different  in  principle/  If  high-frequency  oscilla- 
tions are  induced  (lo^  per  second)  in  a  circuit  containing 
a  condenser  and  a  detector  (spark-gap),  and  the  beaker 
{B,  Fig.  2),  encircled  by  a  coil  of  wire  forming  part  of 


Fig.  2. — C,  condenser;    V,  beaker  containing  suspension  of  corpuscles;   G,  spark- 
gap;  S,  coil  in  which  current  is  induced  (Hober,  loc.  cit.). 

the  circuit,  is  filled  with  a  conducting  solution,  the  oscilla- 
tions are  damped.  Hober  again  found  that  cells  sus- 
pended in  sugar  solution  produce  this  effect,  and  to 
the  same  degree  whether  they  are  intact  or  cytolyzed 
with  saponin,  although  the  Kohlrausch  conductivity 
is,  of  course,  much  greater  in  the  latter  case.  The 
low  Kohlrausch  conductivity  of  intact  cells  is  thus 
apparently  due  to  the  inclosing  plasma  membranes; 
the  internal  conductivity  of  the  protoplasm  is  high. 
Again  by  comparing  the  effects  produced  by  cell- 
suspensions  with  those  produced  by  salt  solutions  of 

^  Hober,  Arch.  ges.  Physiol.,  CXLVIII  (1912),  189. 


PROTOPLASMIC  STRUCTURE  125 

known  conductivity,  Hober  found  that  the  suspension 
gave  the  same  effect  as  a  NaCl  solution  of  a  concentra- 
tion similar  to  that  of  blood  plasma  (i.e.,  between  o.i 
and  0.4  per  cent).     Further  accuracy  is  not  possible. 

Hober  also  used  the  method  of  measuring  the  con- 
ductivity of  cells  by  means  of  rapidly  oscillating  cur- 
rents.^ According  to  theory,  we  should  expect  that  the 
higher  the  oscillatory  frequency  the  less  difference  would 
the  presence  of  the  membrane  make.  Under  the  condi- 
tions, frog's  muscle,  which  had  been  washed  thoroughly 
in  sugar  solution,  behaved  as  if  it  had  a  conductivity 
between  o.i  and  0.2  NaCl;  the  greater  the  frequency 
of  alternation  the  greater  the  conductivity.  This  is 
readily  understood  if  we  reflect  that  when  the  carriers 
of  the  current  (ions)  have  to  pass  through  only  ver>' 
short  distances,  they  are  not  impeded  in  their  movements 
by  the  membrane. 

From  the  results  of  the  experiments  above  Hober 
reaches  the  following  conclusion:^  ''It  can  be  regarded 
as  certain  that  the  blood  corpuscles  possess  a  very  con- 
siderable internal  conductivity,  even  when  the  external 
conductivity  is  minimal;  i.e.,  that  free  ions  are  present 
in  their  interiors,  and  that  these  are  prevented  from  reach- 
ing the  outside  only  by  the  presence  of  a  barrier  to 
diffusion";  i.e.,  the  plasma  membrane. 

The  observations  cited  by  Kite^  and  others,  as  indi- 
cating the  impermeability  of  the  internal  protoplasm 
to  diffusing  substances,  are  probably  to  be  explained  as 
indicating   the  rapidity  with  which   a   scmi-pcnncable 

'Hober,  Arch.  ges.  Physiol.,  CL  (1913),  i5- 

2  Hober,  Physikalische  Chemieder  Zelle  und  dcr  Gewebe  (1914^  P-  3 -"^ 5- 

3  Kite,  Biological  Bulletin,  XXV  (19 13).  i- 


126    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

barrier  is  formed  at  any  free  surface  of  living  protoplasm/ 
This  property  of  forming  fresh  semi-permeable  surface 
films  at  exposed  protoplasmic  surfaces  has  long  been 
known.  NageH^  describes  experiments  with  the  root 
hairs  of  Hydrocharis;  by  crushing  these  structures 
under  a  cover-glass  the  protoplasm  may  be  expressed  in 
the  form  of  separate  rounded  vacuolated  masses.  Each 
of  these  shows  the  same  osmotic  properties  as  the  original 
entire  protoplast;  i.e.,  shrinks  in  hypertonic  solutions, 
resists  the  entrance  of  dyes  (during  the  living  state), 
and  in  general  behaves  as  if  it  were  surrounded  with  a 
semi-permeable  membrane.  Such  an  experiment  might 
also  be  regarded  as  indicating  the  impermeability  of  all 
parts  of  the  protoplast  to  dissolved  substances.  But  it 
can  be  simulated  by  the  simple  experiment  of  breaking 
or  cutting  up  a  large  drop  of  an  insoluble  liquid,  such  as 
chloroform,  in  a  protein-containing  medium;  each  result- 
ing droplet  remains  separate  and  exhibits  the  same 
properties  as  the  original  droplet,  and  the  effect  can  be 
shown  to  depend  on  the  rapid  formation  of  a  thin  protein 
adsorption-film  at  the  surface  of  each  newly  formed 
droplet.  In  a  somewhat  similar  manner,  although  the 
conditions  are  more  complex,  Hving  protoplasm  forms 
films  at  surfaces  which  are  freshly  exposed  by  cutting 
or  other  injury;  this  property  is  shown  only  during  life 
and  is  presumably  a  manifestation  of  the  normal  property 
of  construction  and  repair,  which  is  dependent  on  meta- 
bolic synthesis,  as  we  have  seen.  This  is  indicated  by  an 
experiment  of  Pfeffer's,^  in  which  root  hairs  are  placed  in 

^  Cf.  Chambers,  Jour.  Gen.  Physiol.,  V  (1922),  189. 
^Nageli,  Pjlanzenphysiologische  Studien,  Zurich  (1885). 
^Osmotische  Untersuchungen  (1877),  p.  136. 


PROTOPLASMIC  STRUCTURE  127 

a  weak  solution  of  acid,  which  kills  the  cells.  If  then 
they  are  placed  in  a  weakly  h}'potonic  solution  containin<,' 
dye,  the  latter  immediately  enters  as  soon  as  the  cell 
swells;  i.e.,  the  continuity  of  the  plasma  membrane  is 
then  no  longer  automatically  maintained  (as  in  living 
cells)  when  the  membrane  is  stretched  or  ruptured. 

Presumably  in  living  protoplasm  both  metabolic 
and  purely  physical  factors  (adsorption)  take  part  in 
the  formation  of  new  surface-films.  There  is  evidence 
that  the  protoplasmic  surface-films  undergo  a  change 
in  their  physical  properties  soon  after  they  are  formed; 
this  is  wxll  showm  in  the  freshly  cut  surfaces  of  sea-urchin 
eggs.  Kiister  found  that  the  protoplasm  of  plant 
cells  could  be  broken  into  fragments  by  strong  plas- 
molysis;  these  fragments  at  first  readily  unite  or  cohere, 
but  later  lose  this  property/  In  the  coalescence  of  frag- 
ments of  inert  inorganic  material  a  similar  behavior  has 
been  observed;  freshly  formed  surfaces  reunite  readily, 
but  not  older  surfaces ;  apparently  the  progressive  deposi- 
tion or  adsorption  of  foreign  materials  at  the  surfaces 
alters  their  properties  and  prevents  fusion.''  There  is 
also  evidence  that  the  formation  of  new  surface-films 
plays  an  essential  part  in  the  normal  return  of  irritable 
cells  to  the  resting  state  after  stimulation;  during  the 
period  of  recovery  of  excitability  (refractory  period)  the 
cell-surface  is  apparently  the  seat  of  progressive  changes 
of  this  kind  (see  below  under  refractory  period). 

Hober  cites  the  case  of  myxomycetes  possessing  a 
clear  surface  hyaloplasm  and  a  granular  interior;^  when 

'Kiister,  Ber.  deutsch.  hotan.  Ges.,  XXVII  (1909),  589. 

2  For  an  account  of  these  phenomena  cf.  Bancroft's  Applied  Colloid 
Chemistry,  chap,  v,  on  coalescence. 

3  Hober,  op.  cit.  (1914),  p.  64. 


128    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

the  cell  swells  in  hypotonic  solution  the  thickness  of  the 
hyaloplasm  remains  constant;  apparently  this  thick- 
ness is  regulatively  maintained  by  the  transformation  of 
material  derived  from  the  internal  protoplasm.  Cham- 
bers' observations  on  marine  eggs  show  many  interesting 
instances  of  the  formation  of  films  at  cut  surfaces  or  at 
the  surfaces  of  protoplasmic  fragments;  regions  where 
the  protoplasm  is  broken  down  by  mechanical  or  other 
injury  soon  become  delimited  by  films  bounding  them 
from  the  adjoining  unaltered  protoplasm.^  In  the 
formation  of  artificial  vacuoles  by  the  injection  of 
solutions  into  egg  cells  through  micro-pipettes,  films 
with  semi-permeable  properties  are  formed  about  the 
introduced  droplets.^  The  composition  of  the  salt 
solution  is  an  important  factor  in  the  formation  of  such 
vacuoles;  Chambers  has  recently  shown  that  pure  solu- 
tions of  NaCl  diffuse  into  the  protoplasm  without 
forming  films,  while  if  sufficient  CaClz  is  present,  each 
droplet  of  solution  surrounds  itself  with  a  definite  film 
and  forms  a  vacuole.  A  recent  study  by  Seifriz^  of 
the  physical  properties  of  protoplasm,  as  exhibited  under 
micro-dissection,  gives  many  interesting  details  on  film- 
formation  by  living  protoplasm  under  various  con- 
ditions. 

De  Vries  showed  in  1885"^  that  the  normal  vacuoles 
of  plant  cells  are  surrounded  by  membranes  having  the 
same  osmotic  properties  as  the  plasma  membranes 
(those  inclosing  the  entire  protoplast).     In  his  experi- 

^  Chambers,  loc.  cit.  ' 

*  Kite,  loc.  cit.;  Chambers,  Jour.  Gen.  Physiol.,  V  (1922),  189. 

3  Seifriz,  loc.  cit. 

^Jahrb.  wiss.  Botanik,  XVI  (1885),  465. 


PROTOPLASMIC  STRUCTURE  129 

merits  the  cell  was  placed  in  a  10  per  cent  solution  of 
KNO3  containing  some  eosin  to  serve  as  indicator  of 
permeability;  the  outer  protoplasm  dies  in  one  or  two 
hours  and  becomes  colored,  but  the  vacuole  remains  at 
first  clear  and  uncolored,  showing  impermealjilit)-  of  its 
membrane  to  the  dye.  Later  the  membrane  becomes 
permeable  to  the  dye,  presumably  as  a  result  of  death- 
changes,  and  the  vacuole  contents  become  colored. 
Isolated  vacuoles  show  osmotic  properties  similar  to 
those  of  the  whole  protoplast.  The  observations  of 
Kite  and  Chambers  on  artificial  vacuoles  in  sea-urchin 
eggs  illustrate  the  same  phenomenon,  the  limiting  surface- 
film  of  the  vacuole  having  apparently  the  same  properties 
as  the  surface-film  of  the  entire  cell. 

The  evidence  just  cited  shows  the  error  of  regarding 
the  properties  of  continuous  protoplasm  as  identical 
with  those  of  partitioned  protoplasm.  At  boundar\^ 
surfaces  of  whatever  kind  the  living  substance  exhibits 
special  properties,  in  particular  a  high  resistance  to  the 
diffusion  of  water-soluble  substances  including  ions. 
On  the  other  hand,  the  internal  protoplasm  appears  (at 
least  in  many  cases)  to  be  freely  penetrable  to  diffusing 
substances  of  low  molecular  weight  and  to  ions;  hence 
it  possesses  a  considerable  electrical  conductivit}-.  This 
latter  conclusion  is  of  great  importance  for  the  theory  of 
stimulation  and  conduction,  as  will  be  seen  below. 

As  additional  evidence  for  the  permeability  of  con- 
tinuous or  unpartitioned  protoplasm  to  water-soluble 
substances,  we  may  cite  the  t}^e  of  distribution  shown 
by  many  diffusible  substances  in  cells,  ^lany  such  sub- 
stances are  concentrated  in  special  regions  or  structures, 
in  which  they  appear  to  be  held  in  chemical  or  other 


I30    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

combination;  a  good  illustration  is  the  water-soluble  red 
pigment  of  Arbacia  eggs,  echinochrome,  which  is  con- 
tained chiefly  in  minute  round  chromatophores  scattered 
throughout  the  protoplasm.  That  this  material  is  free 
to  diffuse  is  shown,  however,  by  the  fact  that  cytolytic 
action,  even  temporary,  causes  its  rapid  diffusion  into 
the  surroundings;  and  complete  loss  of  pigment  may 
thus  result.  The  localization  or  condensation  of  the 
pigment  in  the  chromatophores  indicates  apparently 
that  it  is  present  there  in  some  form  of  loose  chemical 
combination  or  adsorption;  but  in  any  such  case  an 
equilibrium  between  the  adsorbed  and  the  dissolved 
compound  must  exist  (Cads  =  KCs{?).  Presumably  the 
dissolved  portion  of  the  pigment  is  homogeneously 
distributed  throughout  the  protoplasm,  hence  the 
chromatophores  adsorb  (or  combine)  equal  quantities 
and  are  similar  in  appearance.  But  any  local  decrease 
in  the  concentration  of  dissolved  pigment,  due  to  diffusion 
through  the  altered  plasma  membrane,  disturbs  the 
adsorption  equilibrium  and  leads  to  the  liberation  of  the 
adsorbed  pigment,  which  may  thus  be  completely  lost 
from  the  cell.  The  conditions  are  similar  in  any  other 
case  of  reversible  adsorption. 

Hermann's  observations  on  the  difference  between  the 
transverse  and  the  longitudinal  conductivity  of  nerve 
fibers  also  indicate  the  higher  conductivity  of  non- 
partitioned  protoplasm  as  compared  with  partitioned. 
He  found  that  the  current  encounters  several  times  the 
resistance  when  the  fibers  are  placed  transversely  between 
the  electrodes,  as  compared  with  fibers  arranged  length- 
wise, with  equal  distances  between  the  electrodes  and 
equal  sectional  areas  of  tissue.     The  same  is  true  for 


PROTOPLASMIC  STRUCTURE  131 

muscle.^  This  result  indicates  again  that  the  inter- 
posed plasma  membranes  offer  a  high  resistance  to  the 
movement  of  ions,  while  the  resistance  of  the  continuous 
protoplasm  is  relatively  slight."^ 

^Hermann,  Arch.  ges.  Physiol.,  V  (1872),  223.  The  character  of 
the  intercellular  partitions  and  their  arrangement  will,  of  course,  afTcct 
the  inner  conductivity  of  the  cell,  but  regarding  these  conditions  we  have 
little  information  at  present. 

2  Compare  the  conclusions  of  Stewart  (/.  Pharmacol,  and  Expcr. 
Therapeutics,  I  [1909],  49);  also  Chambers  (1922),  loc.  cit. 


CHAPTER  VII 

GENERAL  CONDITIONS  DETERMINING  THE 
PROPERTIES  OF  PROTOPLASMIC  MEMBRANES 

Overton's  and  later  researches  have  shown  that  the 
permeability  of  plasma  membranes  to  lipoid-solvent 
substances  is  a  universal  property,  that  the  permeability 
to  water-soluble  substances  of  low  molecular  weight,  not 
soluble  in  organic  solvents,  is  relatively  very  slight,  and 
that  the  ability  of  substances  to  penetrate  most  forms  of 
protoplasm  has  a  close  dependence  on  their  relative  solu- 
bility in  the  two  classes  of  solvents;  i.e.,  on  their  par- 
tition-ratios between  organic  (oil-like)  solvents  and  water. 
The  permeability  for  the  two  classes  of  substances, 
water-soluble  and  '^organo-soluble,"  thus  depends  on 
different  conditions.  It  is  further  significant  that  the 
permeabiHty  for  lipoid- soluble  substances  is  much  less 
variable  than  that  for  the  lipoid-insoluble  substances 
and  water;  the  latter  form  of  permeability  shows  wide 
variations  in  the  same  cell  under  different  physiological 
conditions,  while  the  former  appears  to  undergo  Httle 
change.  The  characteristic  semi-permeability  of  the 
living  plasma  membranes  thus  relates  to  the  lipoid- 
insoluble  group  of  substances;  this  fact,  when  con- 
sidered in  connection  with  the  universal  permea- 
bility to  the  Hpoid-soluble  group,  suggests  that  the 
normal  semi-permeabiHty  depends  on  the  presence  in 
the  membranes  of  water-insoluble  compounds  pos- 
sessing the  solvent  properties  of  organic  solvents. 
The   characteristic   water-insolubiHty    of    the    surface- 

132 


PROPERTIES  OF  PROTOPLASMIC  MEMBRANES     133 

layer  of  protoplasm  is  also  intelligible  on  this  point  of 
view. 

When  we  say  that  a  cell  or  tissue  is  permeable  to  a 
given  substance,  we  state  merely  the  ability  of  the 
substance  to  penetrate;  the  method  of  penetration  is 
not  stated.  Thus  a  dissolved  substance  may  penetrate 
a  partition  by  diffusing  through  the  interspaces,  or  by 
dissolving  in  or  combining  chemically  with  the  substance 
of  the  partition.  In  the  case  of  ions  there  may  be  an 
apparent  penetration  resulting  from  a  change  in  the 
electrical  conditions  at  the  surface  of  the  partition.  For 
example,  when  a  current  is  passed  by  zinc  electrodes 
through  a  bath  of  a  zinc  salt  solution  divided  into  two 
compartments  by  a  zinc  partition,  it  is  not  strictly 
correct  to  say  that  the  zinc  ions  penetrate  the  partition. 
The  effect  is  the  same  as  if  they  did,  but  in  reaUty  zinc 
ions  are  deionized  and  deposited  as  zinc  on  one  face, 
while  from  the  other  face  the  metal  passes  into  solution 
as  zinc  ions.  There  is  apparently  a  penetration  in  such 
a  case,  but  not  in  reality;  and  it  is  possible  that  under 
certain  conditions  the  passage  of  a  current  through  a 
plasma  membrane  may  similarly  depend  on  the  chemical 
combination  of  ions  on  the  one  face  simultaneously 
with  their  release  from  the  other.  The  physical  and 
chemical  conditions  of  these  various  types  of  permeability 
require  careful  examination. 

The  factors  determining  the  penetration  of  dissohed 
substances  through  living  plasma  membranes  are  various, 
and  for  the  purpose  of  the  present  discussion  they  may 
be  grouped  under  the  following  heads:  (i)  structural 
conditions,  including  thickness,  density  (water-content), 
state  of  dispersion  of  structural  colloids,  size  of  interstices 


134    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

or  pores,  (2)  chemical  conditions,  including  special 
composition  and  solvent  properties  of  constituents,  (3) 
physical  conditions  of  other  kinds,  such  as  electrical 
polarization  at  the  faces  of  the  partition  or  other  surfaces, 
electrical  endosmose  effects,  filtration  effects,  and  (4) 
factors  dependent  on  the  Kving  condition  of  the  mem- 
brane, including  variation  of  permeability  due  to  meta- 
bolic or  other  changes;  the  last-named  factors  are 
apparently  the  ones  chiefly  responsible  for  the  active 
types  of  material  transport  in  and  through  cells  in 
absorption  and  secretion  (factors  of  ''physiological 
permeability"). 

A  complete  discussion  of  these  various  factors  need 
not  be  attempted  here,  especially  since  the  whole  subject 
of  permeabiHty  has  recently  been  carefully  reviewed 
in  the  well-known  textbooks  of  BayKss  and  Hober. 
Certain  aspects  of  the  problem  of  permeability  require 
special  consideration,  however,  especially  the  dependence 
of  permeability  on  physical  conditions,  and  the  nature 
of  the  factors  controlling  the  normal  or  physiological 
variations  of  permeability.  The  most  characteristic 
peculiarity  of  the  Kving  protoplasmic  membranes, 
especially  of  irritable  cells,  is  that  their  properties  vary 
with  both  the  external  and  the  internal  conditions,  and 
are  subject  to  regulative  control  of  a  highly  definite 
kind.  Such  properties  cannot  be  derived  from  any 
simple  static  type  of  structure,  or  explained  on  the  basis 
of  the  peculiarities  of  the  colloidal  compounds  composing 
the  membrane.  We  must  recognize  that  the  distinctively 
vital  factors,  those  depending  on  the  metaboHc  activity 
of  the  cell,  are  probably  the  most  important  of  all,  and 
they  are  the  least  understood  at  present.     The  simpler 


PROPERTIES  OF  PROTOPLASMIC  MEMBRANES     135 

physico-chemical  or  non- vital  factors  can,  however, 
be  shown  in  some  cases  to  have  defmite  relations  to 
certain  characteristic  physiological  effects;  e.g.,  in  the 
action  of  salts  and  lipoid-solvent  compounds  on  Hving 
cells.  These  are  the  substances  through  whose  action 
the  physiological  properties  and  activities  of  cells  may 
most  readily  be  altered  in  a  reversible  manner;  and  this 
action  is  referable  in  many  cases  to  a  direct  alteration 
of  the  plasma  membranes. 

PERMEABILITY  AND  STRUCTURAL  CHARACTER 

OF  MEMBRANES 

Semi-permeabiHty  requires  a  certain  closeness  of 
physical  texture;  i.e.,  density  of  structural  material; 
apparently  also  the  structure-forming  substances  must 
be  water-insoluble.  In  all  semi-permeable  artificial 
membranes  water-insolubility  is  essential;  the  most 
perfect  examples  are  the  precipitation-membranes  of  the 
ferrocyanides  and  other  insoluble  salts  of  heavy  metals. 
That  the  chief  compounds  composing  the  plasma 
membranes  are  also  water-insoluble  is  shown  by  the 
characteristic  insolubihty  of  hving  cells  in  their  normal 
aqueous  media. 

The  relation  between  structural  density  and  permea- 
bility in  artificial  membranes  is  well  shown  in  the  ''ultra- 
filters"  devised  by  Bechhold  for  the  separation  of  various 
colloids  from  their  suspension-media.^  These  filters 
consist  of  disks  of  gelatine  hardened  in  formahn.  Bech- 
hold found  that  the  higher  the  coUoid-content  of  these 
partitions,  the  more  numerous  were  the  colloidal  sub- 

■  ^  Bechhold,  Colloids  in  Biology  and  Medicine,  Englisli  translation, 
or  third  German  edition,  1920. 


136    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

stances  which  were  held  back  in  filtration  experiments; 
for  example,  disks  of  10  per  cent  content  prevented  the 
passage  of  nearly  all  the  colloids  employed.  From  such 
facts  we  should  expect  that  a  still  higher  degree  of 
impermeabihty  (to  crystalloids)  would  require  a  higher 
degree  of  structural  density;   i.e.,  lower  water-content. 

Experience  with  artificial  semi-permeable  membranes 
of  copper  ferrocyanide  bears  out  this  expectation;  this 
is  well  seen  in  Morse's  studies  of  these  membranes, 
described  in  his  book,  Aqueous  Solutions.^  He  found 
that  for  the  formation  of  good  semi-permeable  membranes 
an  extremely  fine  porosity  in  the  supporting  porcelain 
cells  was  necessary;  ''excessive  fineness  of  texture  is 
absolutely  indispensable  to  the  correct  measurement  of 
osmotic  pressure"  (p.  15).  A  good  semi-permeable 
membrane  is  thus  essentially  a  fine-textured  structure  of 
water-insoluble  material;  hence  it  resists  the  passage 
of  water  as  well  as  of  dissolved  substances.  Morse  also 
considers  that  the  colloidal  character  of  the  precipitate 
is  an  important  factor  in  semi-permeabihty.  Even 
under  the  best  conditions  a  high  degree  of  semi-permea- 
bility is  difficult  to  obtain  with  precipitation-membranes, 
and  this  property  is  subject  to  change;  it  is  affected  by 
temperature  (cf.  pp.  85-86)  and  especially  by  electrolytes 
(cf.  pp.  91-92)  which  cause  rapid  deterioration  in  the 
membrane.  LiCl  was  the  least  harmful  of  the  electro- 
lytes investigated  (cf.  p.  214)  and  Morse  gives  determina- 
tions of  the  osmotic  pressure  of  this  salt. 

Since  fineness  of  texture  is  favorable  to  semi-permea- 
biHty  (i.e.,  to  the  production  of  osmotic  effects),  one 
might  expect  that  any  insoluble  porous  partition  would 

^  Morse,  Aqueous  Solutions,  Carnegie  Institute  Publications  (1914). 


PROPERTIES  OF  PROTOPLASMIC  IMEjMBRAXES     137 

show  osmotic  action  (semi-permeability)  if  only  its 
pores  were  sufficiently  minute.  In  fact,  Thomas  Graham 
observed  many  years  ago  (1854)  that  certain  hne-graincd 
porcelains  had  definite  osmotic  action.  Recently  the 
pore-diameters  of  osmotically  acting  porcelain  disks 
have  been  investigated  by  Bigelow  and  Bartell,'  and 
well-marked  osmotic  effects  were  found  when  the  pores 
had  a  diameter  of  the  order  0.2-0.35)11.^ 

In  general  we  may  conclude  from  such  facts  that  in 
living  semi-permeable  membranes  the  degree  of  porosity 
is  low;  i.e.,  the  interspaces  between  the  water-insoluble 
colloidal  particles  forming  the  structural  material  are 
at  least  as  small  as  in  porcelain  and  probably  smaller, 
since  Bartell's  membranes  are  not  completely  semi- 
permeable. The  physical  conditions  are  probably  closely 
comparable  with  those  existing  in  well-supported  precipi- 
tation-membranes of  copper  ferrocyanide,  such  as  ]\Iorse 
employed.  In  plasma  membranes,  however,  variations 
in  the  subdivision  of  the  colloidal  constituents  may  cause 
variations  in  the  size  of  the  interspaces,  and  hence  in  the 
permeability.  The  progressive  deterioration  to  which 
artificial  colloidal  membranes  are  subject  in  the  pres- 
ence of  electrolytes  is  apparently  prevented  in  living 
membranes  by  compensatory  factors  dependent  on  me- 
taboHsm;  presumably  any  interruptions  of  continuity  arc 
at  once  automatically  repaired  by  the  formation  or 
deposition  of  new  structural  material  (see  below  under 
stimulation) . 

^  Bigelow,  Journal  of  the  American  Chemical  Society,  XXIX  (igo;), 
1675;  Bartell,  Journal  of  Physical  Chemistry,  XV  (191 0,  659,  and  XVI 
(1912),  318. 

'  Bartell,  loc.  cit.  (191 2). 


138    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

Such  fine- textured  membranes  must  resist  the  passage 
of  water  as  well  as  of  dissolved  substance.  In  Morse's 
experiments  many  days  were  often  required  to  reach 
osmotic  equilibrium.  There  is  also  evidence  that  many 
living  plasma  membranes  offer  a  high  resistance  to  the 
passage  of  water;  i.e.,  are  relatively  water-impermeable. 
This  statement  may  seem  surprising  in  view  of  the  fact 
that  the  passage  of  water  into  and  out  of  living  cells  in 
anisotonic  solutions  is  usually  rapid;  but  the  membranes 
are  extremely  thin  and  the  ratio  of  the  surface  to  the 
inclosed  volume  is  very  large,  so  that  relatively  rapid 
entrance  of  water  is  quite  consistent  with  a  very  low 
specific  permeability  to  the  liquid. 

The  loss  of  semi-permeability  at  death  is  associated 
with  an  increase  of  permeabiHty  to  water  as  well  as  to 
dissolve  substances.  This  is  shown  in  some  experiments 
of  Bernstein  who,  with  another  problem  in  mind  (the 
conditions  under  which  water  is  held  in  cells) ,  determined 
the  relative  rates  of  evaporation  of  water  from  living 
and  dead  tissues.'  Bernstein  used  the  method  (intro- 
duced by  Liebig)  of  measuring  the  ''force  of  imbibition" 
of  membranes.  A  tube  widened  at  one  end  (thistle  tube) 
is  fixed  vertically  with  its  narrow  end  dipping  into 
mercury;  the  tube  is  completely  filled  with  water  and 
the  upper  expanded  end  is  closed  by  the  membrane  under 
examination.  As  water  evaporates  through  the  mem- 
brane the  mercury  rises  in  the  tube,  showing  the  develop- 
ment of  a  pressure;  the  rate  of  evaporation  through  the 
membrane  is  thus  indicated.  Bernstein  used  fine  tubes 
ending  above  in  equally  sized  funnels  which  were  closed 
(A)  with  living  membrane  and  (B)  with  dead  membrane 

^  Bernstein,  Electrohiologie,  Braunschweig  (1912),  pp.  167  £f. 


PROPERTIES  OF  PROTOPLASMIC  MEIMBRANES     139 

(e.g.,  killed  by  heat).  Results  of  the  following  kind 
were  obtained  with  frog  skin: 

(A)  Living  (B)  Dead 

After    4  h ht-     23  (mm.)  52  (mm.) 

6h 85  160 

8h 180  285 

10  h 256  347 

(both  dead) 

22,  h 401  400 

It  is  clear  that  the  rate  of  evaporation  is  much  greater 
through  the  dead  membrane.  Similar  experiments  with 
plant  tissues  (leaves)  gave  similar  results;  von  ]Mohl 
(in  1847)  and  Naegeli  (in  1861)  had  already  called 
attention  to  the  fact  that  frozen  plant  tissues  (leaves, 
fruits)  dried  more  rapidly  than  living.''  Bernstein  experi- 
mented also  w^ith  thin  sheets  of  muscles  (abdominal 
oblique  of  frog),  both  living  and  killed  with  chloroform, 
and  found  that  the  rate  of  evaporation  through  the  Uving 
muscle  was  about  half  of  that  through  the  dead;  the 
difference  was  greatest  during  the  first  hour,  when  the 
living  tissue  was  relatively  normal. 

Bernstein's  conclusion  was  that  living  tissue  has 
greater  water-binding  power  than  dead,  and  he  regarded 
the  electrically  polarized  condition  of  the  plasma  mem- 
branes as  the  chief  factor  hindering  the  outward  passage 
of  water.  Apparently  a  potential  difference  of  the  value 
of  ca.  0.1  volt  exists  normally  between  the  outer  and 
the  inner  surfaces  of  the  plasma  membrane;  this  gradient 
is  positive  externally  and  negative  internally.  Resistance 
is  thus  offered  to  the  passage  of  the  positively  charged 
water  outwardly  across  the  membrane.     This  exphma- 

^  Cf.  Bernstein,  op.  cit.,  p.  170. 


I40    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

tion,  while  ingenious,  does  not  seem  sufficient;  in  muscle 
and  other  living  cells  immersed  in  aniso tonic  solutions 
water  seems  to  pass  with  equal  readiness  in  either  direc- 
tion through  the  membrane;  for  example,  Arhacia  eggs 
in  h>^er-  and  hypotonic  sea  w^ater  shrink  and  swell 
(respectively)  at  about  the  same  rates.^  Hober  refers 
the  difference  observed  by  Bernstein  to  the  greater 
turgor  of  the  living  cells  ;^  this  explanation  also  seems 
doubtful,  since  turgor  is  either  absent  or  shght  in  verte- 
brate tissues.  The  simplest  as  well  as  most  probable 
explanation  is  that  the  permeabihty  to  water  increases 
with  death,  along  with  the  permeability  to  other  sub- 
stances. As  the  plasma  membrane  loses  its  semi- 
permeability,  with  the  associated  fineness  of  texture,  it 
also  loses  its  relative  impermeability  to  water. 

Permeability  to  w^ater  is  one  of  the  little  studied 
properties  of  cells.  Yet  it  is  an  important  property 
which  appears  to  be  constant  for  a  particular  cell  under 
definite  conditions.  There  is  evidence  that  it  varies 
with  the  physiological  state  and  activity  of  the  cell, 
and  in  certain  cases,  especially  in  gland  cells,  the  indica- 
tions are  that  it  is  under  nervous  control.  Thus  when 
the  chorda  tympani  is  stimulated,  the  submaxillary  gland 
secretes  a  copious  watery  saliva;  similarly  the  sweat- 
glands  and  the  kidney  secrete  actively  under  certain 
conditions,  but  not  under  others.  In  most  cases  the 
secretory  substances  leave  the  cell  in  aqueous  solution; 
and  although  the  factors  are  complex,  there  seems  to 
be  little  doubt  that  the  transport  of  the  secretion  across 
the  cell-boundary  is  associated  with  an  increased  permea- 

^  R.  S.  Lillie,  American  Journal  of  Physiology,  XLV  (1918),  406. 
=*  Hober,  op.  cit.,  p.  255. 


PROPERTIES  OF  PROTOPLASMIC  MEIMBRANES     141 

bility  to  water  as  well  as  to  dissolved  substances.  The 
character  of  the  bioelectric  variation  accompanying 
secretion  also  indicates  this. 

Antropoff^  has  studied  the  influence  of  the  water- 
permeability  of  osmometer  membranes  on  the  rate  of 
osmotic  transfer  of  water.  He  reaches  the  general 
formulation : 

i.e.,   the  rate  of  passage  of  water  into  an  osmometer 

'dp\ 

^1  at  any  time  is  proportional  to  the  penncability  of 

the  membrane  to  water  {a)  and  to  the  osmotic  pressure 
of  the  solution  (P)  less  the  hydrostatic  or  other  pressure 
(P/)  resisting  the  transfer.  The  rate  of  osmotic  transfer 
of  water  is  thus  proportional  to  the  product  of  the 
effective  osmotic  pressure  into  the  permeability  to  water. 
This  formulation  defines  the  conditions  for  perfect 
membranes;  i.e.,  those  which  are  permeable  to  water 
and  impermeable  to  solute. 

In  the  Arhacia  egg  the  permeability  to  water  is 
altered  in  a  remarkable  manner  as  a  result  of  fertilization. 
A  quantitative  measure  of  this  pemieability  may  be 
obtained  by  measuring  the  rate  at  which  water  enters 
or  leaves  the  egg  in  dilute  or  concentrated  sea  water. 
This  rate  is  found  to  be  increased  about  fourfold  after 
fertilization,  indicating  that  this  process  is  associated 
with  a  marked  increase  in  permeability  to  water.  If 
mixed  fertilized  and  unfertilized  eggs  are  placed  in  dikite 
or  concentrated  sea  water,  the  former  undergo  change 
of   volume   much   more   rapidly    than    the   Litter,    and 

^  Antropoff,  Z.  physik.  CJiem.,  LXXVI  (191 1),  721. 


142    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

within  a  minute  or  less  the  two  can  easily  be  distinguished 
by  their  difference  in  size.  The  semi-permeability  of 
the  plasma  membrane  is  not  impaired,  although  the 
permeability  to  water  is  increased.  The  conditions  of 
this  phenomenon  are  probably  complex,  and  determined 
by  metabolic  factors  of  unknown  nature.  The  change 
of  permeability  is  progressive  and  occupies  a  considerable 
time,  some  20  minutes  elapsing  (at  20°)  before  it  nears 
its  final  stage;  it  is  arrested  by  anaesthetics  (chloral 
hydrate,  ure thane,  alcohols)  and  by  cyanide  in  higher 
concentrations.^ 

If  the  impermeability  to  water  in  this  cell  is  due  to 
the  presence  of  water-insoluble  substances  (lipoids  or 
cholesterol)  in  the  surface-film,  the  change  above  would 
indicate  that  these  are  altered  or  removed  in  part;  i.e.,  a 
change  in  the  chemical  composition  of  the  surface  layer 
is  to  be  assumed.  The  nature  of  this  change  is  unknown; 
but  Lyon's  observation  that  the  iodine-combining  power 
of  the  egg  is  decreased  after  fertilization^  may  indicate 
a  decrease  in  certain  unsaturated  compounds  which 
would  otherwise  take  up  the  iodine — possibly  cholesterol 
or  unsaturated  lipins  (lecithin).  The  permeability  of 
fertiHzed  eggs  to  water  can  be  artificially  modified  in 
certain  ways;  it  is  decreased  by  anaesthetics  (chloral, 
urethane,  alcohols),^  a  fact  also  indicating  a  dependence 
on  the  lipoid-content  of  the  protoplasmic  surface-film. 

Chambers  finds  certain  differences  in  the  behavior  of 
fertilized   and  unfertilized   echinoderm   eggs  in  micro- 

^  R.  S.  LiUie,  American  Journal  of  Physiology,  XL  (1916),  249; 
XLIII  (1917),  43;  XLV  (1918),  406. 

*Lyon  and  Shackell,  Science,  XXXII  (1910),  249. 

3  R.  S.  Lillie,  American  Journal  oj  Physiology,  XLV  (1918),  427. 


PROPERTIES  OF  PROTOPLASMIC  JMEMBRANES     143 

dissection;^  the  surface  of  the  unfertilized  egg  is  less 
easily  cut  or  torn  with  a  needle,  but  exhibits  less  power 
of  repair  than  that  of  the  fertilized  egg.  This  latter 
difference  is  probably  to  be  correlated  with  the  increased 
rate  of  metaboHsm  following  fertilization;  oxygen- 
consumption,  COz-evolution  and  heat-production  are 
then  greater,^  also  the  susceptibility  to  KCN  poison- 
ing and  other  forms  of  chemical  injury.  Facts  of  this 
kind  illustrate  the  close  correlation  existing  between  the 
physical  state  of  the  plasma  membrane  and  the  physi- 
ological properties  and  metabolic  activity  of  the  cell. 
Other  examples  of  this  correlation  will  be  described 
later,  especially  in  relation  to  stimulation-processes, 
which  are  intimately  associated  with  changes  in  the 
membranes. 

PERMEABILITY  AND  SOLVENT  PROPERTIES  OF 
MEMBRANE  CONSTITUENTS 

It  was  first  pointed  out  by  Nernst  in  1890  that  the 
solvent  properties  of  the  substances  composing  a  mem- 
brane may  determine  the  latter's  penneability  to  dis- 
solved substances,  and  hence  the  production  of  osmotic 
effects.  Thus  when  benzol  is  separated  from  ether  b}-  a 
partition  consisting  of  bladder  membrane  soaked  in  water 
(in  effect  a  layer  of  water),  the  ether,  because  of  its  greater 
solubiUty  in  water,  passes  the  partition  more  rapidly  than 
the  benzol,  and  a  pressure  is  set  up  on  the  benzol  side 
of  the  partition.^     The  membrane  is  impcnneable   to 

'  Chambers,  Proceedings  of  the  Society  of  Experimental  Biology  arid 
Medicine,  XVII  (1919),  41. 

^Cf.  Shearer,  Proceedings  of  the  Royal  Society,  B,  XCIII  (1921), 
213,  410. 

3  Nernst,  Z.  physik.  Chcm.,  VI  (1890),  37. 


144    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

benzol,  which  is  almost  insoluble  in  water,  while  ether 
is  readily  soluble  (to  the  extent  of  about  12  volumes 
per  cent)  and  penetrates  the  partition.  Experiments 
illustrating  the  same  principle  may  be  performed  with 
gases;  thus  if  a  tube,  containing  air,  closed  below  with 
a  water-soaked  membrane  and  connected  above  with  a 
manometer,  is  placed  in  a  vessel  of  ammonia  or  hydro- 
chloric acid  gas,  the  pressure  rapidly  rises  in  the  tube 
because  of  the  penetration  of  the  water-soluble  gas 
through  the  water-layer.  Ramsay's  well-known  experi- 
ment with  a  tube  filled  with  nitrogen  and  separated 
from  a  hydrogen  atmosphere  by  a  palladium  partition 
(at  350°  to  400°)  illustrates  the  same  general  phenomenon; 
hydrogen  but  not  nitrogen  penetrates  the  partition, 
hence  the  pressure  rises  within  the  tube.^ 

In  all  of  these  cases  the  permeability  of  the  partition 
depends  on  its  consisting  (in  part)  of  some  material 
which  acts  as  a  solvent  to  the  penetrating  substance. 
Nernst  called  attention  to  the  possibility  that  similar 
conditions  might  exist  in  living  cells;  i.e.,  that  the 
solubility  of  substances  in  constituents  of  the  proto- 
plasmic membranes  might  be  the  condition  of  their 
selective  absorption  by  cells;  and  this  form  of  explanation 
was  later  adopted  by  Overton  who  reached  the  conclu- 
sion, as  a  result  of  his  studies  on  permeability  already 
described,  that  the  protoplasmic  surface  layer  consisted 
chiefly  of  compounds  with  solvent  properties  similar  to 
those  of  typical  organic  solvents. 

Later,  chiefly  because  of  experiments  indicating  a 
parallelism  between  the  penetration  of  various  acid  and 
basic  dyes  into  living  cells  and  the  solubility  of  the  same 

^  Ramsay,  Z.  physik.  Chem.,  V  (1894),  518. 


PROPERTIES  OF  PROTOPLASMIC  JMEiMBRAXES     145 

dyes  in  solutions  of  lecithin  and  cholesterol,'  Overton 
referred  the  characteristic  permeability  of  the  plasma 
membrane  specifically  to  the  presence  of  Hpoids.  1'his 
evidence  is  in  itself  scarcely  conclusive,  especially  since 
other  factors  are  now  known  to  be  of  importance  in  the 
penetration  of  dyes  into  cells,  and  many  exceptions  ha\'c 
been  found  to  the  rule  that  lipoid-solubiHt}-  connotes 
ready  penetration.  The  state  of  colloidal  suljdivision 
has  been  shown  to  be  an  important  factor,^  and  the 
negative  electrification  of  the  cell-surface  must  also 
play  a  part  by  favoring  the  adsorption  and  penetration 
of  the  positive  particles  of  the  basic  dyes,  which  Overton 
found  to  penetrate  most  readily.  But  other  evidence 
of  various  kinds  supports  Overton's  conclusion  in  the 
main;^  and  there  can  be  Kttle  doubt  that  the  lipoids 
form  essential  constituents  of  plasma  membranes,  even 
although  other  compounds,  especially  proteins,  may  be 
of  equal  importance;  e.g.,  as  furnishing  a  structural 
support  to  the  lipoids.  The  influence  of  lipoid-solvents 
on  the  permeability  and  activity  of  cells,  the  character- 
istic cytolytic  action  of  these  compounds,  the  influence 
of  salt-solutions  on  oil-water  emulsions,  the  peculiar 
relations  of  cholesterol  to  the  mechanical  properties  of 
the  plasma  membranes,  the  properties  of  artificial  lii)oid- 
impregnated  membranes,  and  many  other  facts  all 
indicate  the  important  role  of  lipoids  in  determining  the 
properties  of  plasma  membranes.     It  is  not  to  be  con- 

^  Overton,  Arch.  ges.  Physiol.^  XCII  (1902),  115. 
^  Ruhland,  loc.  cit. 

3  Especially  the  results  with  strong  and  weak  acids  and  bases,  above 
cited.  Cf.  the  discussion  in  chap,  viii,  pp.  428  ff.,  of  Hobcr's  Physikalischc 
Chemie  der  Zelle. 


146    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

eluded  that  these  membranes  are  simple  continuous 
sheets  of  lipoid;  the  very  fact  that  their  properties  are 
complex  and  vary  from  species  to  species  is  inconsistent 
with  any  such  simple  view,  and  the  existence  of  specific 
cytolysins  may  indeed  be  taken  as  proof  that  proteins 
form  an  essential  part  of  their  composition.  In  fact, 
as  already  pointed  out,  the  plasma  membrane  is  not  to 
be  regarded  as  a  simple  passive  layer  of  colloidal  or 
other  material,  but  rather  as  a  special  living  structure 
with  a  characteristic  metabolism  of  its  own,  and  with 
both  its  physical  and  chemical  properties  modified  in 
correspondence  with  its  situation  at  the  cell-boundary. 
All  that  can  safely  be  maintained  is  that  its  properties 
are  intimately  dependent  on  the  properties  of  its  lipoid 
constituents,  hence  vary  with  changes  in  the  physical 
and  chemical  state  of  the  latter.  It  will  be  unnecessary 
to  review  in  further  detail  the  large  body  of  experimental 
fact  indicating  the  presence  of  lipoids  in  the  surface-films 
of  cells;  this  evidence  is  discussed  at  length  with  full 
references  to  the  literature  in  Hober's  and  Bayliss' 
textbooks. 

PERMEABILITY  AND  PHYSICAL,  ESPECIALLY 
ELECTRICAL,  CONDITIONS 

Of  late  years  electrical  conditions  have  been  shown 
to  be  of  great  importance  in  determining  the  permeability 
of  artificial  partitions  (parchment,  porcelain,  and  other 
substances),  and  from  general  principles  it  seems  certain 
that  such  factors  must  play  a  corresponding  part  in 
the  protoplasmic  membranes.  In  artificial  membranes 
two  factors  have  been  shown  to  be  of  importance:  (i) 
the  potential-difference  between  the  solutions  in  contact 


PROPERTIES  OF  PROTOPLASMIC  MEiMBR^VNES     147 

with  the  opposite  faces  of  the  partition,  and  (2)  the 
potential-difference  between  the  solid  or  c()lloi(hd 
material  composing  the  partition  and  the  Huid  occu])ying 
its  interstices  or  pores.'  The  influence  of  these  electrical 
factors  is  shown  with  especial  clearness  in  the  phenomena 
of  electrical  endosmose,  and  in  the  related  phenomenon  of 
negative  or  anomalous  osmosis.  In  both  phenomena  an 
electrified  layer  of  fluid  (occupying  the  pores  of  the 
partition,  hence  in  contact  with  the  surface  of  the 
structural  material)  is  situated  within  the  electrical 
field  between  the  two  surfaces  of  the  partition;  the 
fluid  is  accordingly  transported  across  the  partition  by 
electrostatic  attraction  in  one  or  the  other  direction,  so 
long  as  the  electric  conditions  remain  unchanged.  The 
work  involved  in  the  transport  is  electrical;  in  negative 
osmosis  the  electrical  field  is  maintained  by  the  unequal 
diffusion-rates  of  the  ions  of  the  solution  bathing  the 
partition;  in  electrical  endosmose  by  the  external 
current  traversing  the  partition. 

It  will  be  evident  that  under  these  conditions  the 
permeability  of  the .  partition  to  electrified  material, 
whether  water,  colloidal  particles,  or  ions,  will  be  different 
in  the  two  directions.  Water,  for  example,  will  diffuse 
outward  in  an  osmometer,  i.e.,  from  the  more  to  the  less 
concentrated  solution,  when  the  electrical  diffusion  field 
is  oriented  in  such  a  way  that  the  charged  layer  of  fluid 
in  the  pores  is  attracted  outwardly  with  sufticient  force 
to  overcompensate  the  purely  osmotic  effect.  'Hiis 
condition  is  met  when   a  stronger  solution  of  IICl  is 

'  Girard,  CompLrend.,  CXLVI  (1908),  927;  CXLVllI  (1909),  1047; 
/.  de  Physiol,  et  de  Path,  gen.,  XII  (1910),  471;  /.  dc  Chitn.  d  dc  Phys. 
XVII  (1910),  383. 


^ 


148  pbS^Q£lasmic  action  and  nervous  action 

parai|^froin  a  weaker  solution  by  a  porcelain  partition; 
)lution  on  the  more  dilute  side  is  then  positive, 
^  b^ause  of  the  diffusion  field;  the  solid  substance  of 
,  the  partition  is  positive  and  the  water  in  the  pores  is 
negative;  accordingly  the  latter  is  drawn  toward  the 
more  dilute  solution.  Anomalous  osmosis  of  this  kind 
has  long  been  known;  Graham  (1854)  observed,  for 
example,  that  K2SO4  showed  positive  osmosis  in  alkaline 
solution  and  negative  in  acid  when  a  bladder  membrane 
was  used;  NaCl,  on  the  contrary,  showed  positive  osmosis 
in  acid  solution  and  was  indifferent  in  neutral  solution.^ 
These  changes  in  the  direction  of  transport  are  now 
recognized  as  depending  on  the  influence  of  the  ions  on 
the  charged  condition  of  the  structural  surfaces.  Many 
surfaces  are  rendered  positive  by  H  ions  and  polyvalent 
cations;  the  adjacent  water-layer,  being  then  negative, 
moves  in  a  corresponding  direction  in  the  potential- 
gradient  between  the  two  surfaces  of  the  membrane. 
Water  may  thus  move  in  one  or  the  other  direction 
according  to  the  electrolyte  content.  The  influence  of 
ions  on  the  direction  of  transport  is  shown  with  especial 
clearness  in  the  experiments  of  Perrin^  and  others  on 
electrical  endosmose.  The  influence  of  ions  on  anomalous 
osmosis  has  recently  been  studied  by  Loeb,  using  gelatine- 
permeated  membranes  of  collodion;  the  effect  varies 
with  the  Ph  of  the  solution  and  becomes  minimal  at  the 
isoelectric  point  of  gelatine.     Isoelectric  membranes  can, 

^  Graham,  Phil.  Trans.,  CXLIV  (1854),  117.  For  a  recent  account 
of  negative  osmosis  cf.  Bartell,  Journal  of  the  American  Chemical  Society, 
XXXVI  (1914),  646;  BarteU  and  Hocker,  ibid.,  XXXVIII  (1916), 
1029,  1036;  Bartell  and  Madison,  Journal  of  Physical  Chemistry^ 
XXIV  (1920),  444,  593. 

2  Perrin,  loc.  cit. 


PROPERTIES  OF  PROTOPLASMIC  :MEMBRAXKS     149 

however,  become  charged  and  exhibit  anomalous  osmosis 
under  the  influence  of  trivalent  ions.' 

The  transport  of  the  ions  of  salts,  and  consequently 
the  permeability  of  a  given  membrane  to  a  diffusing  salt, 
are  similarly  affected  by  the  electrical  state  of  the 
partition,  and  this  influence  has  recently  been  studied  by 
Girard,  using  bladder  membranes.  If  the  polarization 
of  the  membrane  (P.D.  between  its  opposite  faces)  has 
a  certain  orientation,  the  penetration  of  a  salt  like 
MgCli  or  Na2S04  in  the  one  direction  is  facilitated,  in 
the  other  direction  hindered.^ 

The  application  of  the  principles  above  to  the  case 
of  the  plasma  membrane  is  somewhat  uncertain,  since 
the  structure  of  the  latter  is  in  many  respects  different 
from  that  of  fixed  porous  membranes  of  macroscopic 
dimensions.  Yet  variations  in  the  P.D.  across  the  plasma 
membrane  must  have  a  corresponding  effect  on  the 
permeability;  this  effect,  however,  is  probably  accom- 
panied in  living  protoplasm  by  other  effects,  such  as 
chemical  effects  depending  on  the  electrode-Hke  action 
of  the  membrane,  and  effects  on  colloidal  dispersion. 
There  is  no  doubt  that  the  permeabihty  of  many  plasma 
membranes,  especially  of  irritable  cells,  is  very  sensitive 
to  changes  of  electrical  condition;  thus  the  turgor 
motors  of  plants  {Mimosa,  DioncBo)  depend  for  their 
action  upon  variations  of  permeability,  which  arc 
readily  induced  by  the  electric  current.  The  passage 
of  a  current  through  a  muscle  or  nerve,  in  such  a  way  as 
to  decrease  locally  the  resting  polarization  of  the  cell- 

^  Cf.  J.  Loeb,  Jour.  Gen.  Physiol,  IV  (1922),  463,  and  earlier  refer- 
ences there  given. 

^  Girard,  Jour,  de  Physiol,  et  de  Path,  gen.,  loc.  cit. 


I50    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

surface  (i.e.,  cause  depolarization),  causes  stimulation, 
which,  as  will  be  shown  below,  is  attended  with  an 
increase  of  permeability.  We  must  conclude  that 
electrical  factors  are  of  great  importance  in  determining 
the  properties  of  Hving  plasma  membranes;  variations 
in  the  external  electrical  conditions  occasion  correspond- 
ing variations  in  the  membrane,  and  with  these  are 
connected  various  physiological  effects.  The  polar 
disintegration  shown  by  various  cells  through  which 
currents  are  passed  also  indicates  a  direct  action  on  the 
membrane;  the  character  of  this  action  is  determined  by 
the  direction  of  the  current.  The  law  of  polar  stimulation 
is  the  expression  of  similar  conditions  in  irritable  tissues.^ 
The  physiological  effects  of  salts  and  electrolytes  are 
undoubtedly  to  be  referred  largely  to  changes  in  electrical 
conditions,  as  shown  by  the  numerous  parallels  between 
the  action  of  salts  in  purely  physical  phenomena  like 
electrical  endosmose  or  change  of  colloidal  aggregation, 
and  their  action  on  vital  activities  of  various  kinds. 

'  Cf.  chapter  on  stimulation. 


CHAPTER  Mil 

RELATION  OF  THE   INORGANIC   SALTS   OF  THE 
MEDIUM  TO  THE  PHYSIOLOGIC.\L  PROCESSES 
IN  PROTOPLASM 

The  relation  of  the  inorganic  salts  present  in  the 
external  medium  to  the  properties  and  activities  of 
living  cells  has  been  the  subject  of  much  investigation 
since  Ringer's  time,  and  the  present  brief  account  \vill 
be  confined  to  the  more  general  and  fundamental  rela- 
tions of  this  kind,  especially  those  indicating  that  the 
chief  basis  of  the  physiological  action  of  the  salts  of 
the  medium  is  their  action  upon  the  protoplasmic  surface 
layers.  Since  much  of  the  pioneer  work  in  this  field  is 
due  to  Overton,  and  since  many  of  the  results  of  his 
studies  are  applicable  to  living  protoplasm  in  general, 
I  shall  first  give  a  somewhat  detailed  summary-  of  his 
earlier  experiments  on  the  action  of  salt  solutions  on 
the  muscle  and  nerve  of  frogs. ^ 

Overton  first  examined  carefully  the  well-known 
effect,  reversible  loss  of  irritability  in  isotonic  solutions 
of  indifferent  non-electrolytes  such  as  sugar,  using  small 
muscles;  e.g.,  sartorius,  cutaneus  pectoris,  and  foot 
muscles.  He  found  that  all  indifferent  non-electrolytes, 
independently  of  their  special  composition  (dextrose, 
sucrose,  lactose,  erythrite,  mannite,  alanin,  taurin,  and 
asparagin),  produce  this  effect.  The  action  is  not 
poisonous,  since  the  addition  of  a  small  proportion  of  an 
isotonic  solution  of  sodium  chloride  to  the  non-electroKte 

» Overton,  Arch.  ges.  Physiol.,  XCII  (1902),  346;   CV  (1904),  176. 

151 


152    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

solution  prevents  the  loss  of  irritability;  the  inference  is 
therefore  justified  that  the  effect  depends  upon  a  with- 
drawal of  electrolytes,  especially  sodium  chloride,  from 
the  tissue.  That  the  electrolytes  thus  removed  come 
almost  entirely  from  the  interstitial  spaces  of  the  tissue, 
and  not  from  the  interior  of  the  cells,  was  later  proved 
by  Urano  and  Fahr.^  The  important  conclusion  follows 
that  the  presence  of  electrolytes  (salts)  in  the  external 
medium  is  essential  to  the  normal  irritability  of  the  cell. 

Overton  discusses  the  question  whether  the  removal 
of  sodium  salts  acts  by  preventing  the  conduction  of 
stimulation  or  by  deranging  the  contractile  mechanism 
of  the  cell.  Biedermann  had  previously  shown  that 
after  incorporation  of  sufficient  water  in  hypotonic  salt 
solution,  a  muscle  may  lose  the  power  of  contraction 
without  losing  that  of  conducting  stimuli.^  By  immers- 
ing a  portion  of  a  sartorius  in  isotonic  sugar  solution, 
Overton  showed  that  stimuli  are  not  transmitted  through 
the  salt-free  muscle.  It  is  known  that  a  muscle  deprived 
of  irritability  in  sugar  solution  will  shorten  in  solutions 
of  chloroform  or  other  cytolytic  substances;  presumably, 
therefore,  the  contractile  mechanism  is  structurally 
intact,  but  fails  to  act  in  the  absence  of  electrolytes 
because  of  the  failure  of  conduction.  Without  the  power 
of  transmitting  stimuli,  the  muscle  is  unable  to  contract 
as  a  whole. 

The  least  concentration  of  NaCl  required  for  the 
maintenance  of  irritability  was  determined  by  using 
mixtures  of  isotonic  sugar  solution   (6  per  cent)   and 

'Urano,  Z.  BioL,  L  (1907),  212;  LI  (1908),  483;  Fahr,  Z.  Biol., 
LII,  72. 

»  Biedermann,  Ber.  Akad.  Wiss.  Wien,  XCVII  (1888),  loi. 


INORGANIC  SALTS 


153 


NaCl  solution  (0.7  per  cent).  No  sij^mificant  decline  in 
irritability  was  found  until  the  salt-content  fell  below 
0.15  per  cent.  At  o.i  per  cent  irritability  was  distinctly 
less  than  normal,  and,  with  further  decrease  in  concentra- 
tion, it  declined  rapidly,  becoming  zero  at  about  0.07 
per  cent.  In  mixtures  containing  less  than  0.07  per 
cent  NaCl  irritability  was  lost  as  rapidly  as  in  i)ure 
sugar  solution.^  The  time  required  for  complete  loss  of 
irritabihty  thus  represents  the  time  required  for  diffusion 
to  reduce  the  NaCl  of  the  intercellular  spaces  to  this 
concentration. 

Sugar-treated  muscles  rapidly  regain  irritability  in 
solutions  of  all  Na  salts.  The  nature  of  the  anion 
associated  with  the  Na  was  found  to  be  indifferent, 
provided  it  was  not  too  toxic;  with  most  salts  the 
minimal  concentration  for  the  maintenance  of  irritability 
was  about  the  same  as  with  NaCl.  Apparently,  there- 
fore, it  is  the  Na  ion,  and  not  the  undissociated  molecule 
or  the  anion,  which  is  responsible  for  the  maintenance 
of  irritability.  A  definite  function,  that  of  preserving 
the  normal  irritability  of  muscle  and  nerve,  is  thus  to  be 
ascribed  to  the  Na  salts  in  blood  plasma;  their  role  is 
not  merely  osmotic,  as  formerly  supposed.^  This  rela- 
tion of  Na  ions  to  irritabihty  and  contractility  is  a 
specific  peculiarity  of  muscle  cells;  the  conditions  in 
other  contractile  forms  of  protoplasm  are  often  wideh- 
different;     thus   the   contraction   of   cilia,    spermatozoa 

1  This  effect  apparently  varies  with  oxygen  tension.  Pond  has 
recently  shown  that  in  solutions  saturated  with  oxygen  tlie  NaCI  content 
may  be  reduced  to  less  than  .05  per  cent  without  loss  of  irritability: 
Jour.  Gen.  Physiol.,  Ill  (1921),  807. 

2  Cf.  also  J.  Loeb,  "On  the  Production  of  Rhythmical  Contractions 
in  Muscles  by  Ions,"  Festschrift  fur  Fick  (1899),  p.  loi. 


154   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

and  protozoan  structures  like  the  stalk  of  Vorticella 
is  independent  of  Na  ions  in  the  medium;  cilia,  in  fact, 
often  exhibit  prolonged  and  vigorous  activity  in  media, 
like  isotonic  KCl  or  MgCL  which  rapidly  and  completely 
abolish  irritability  in  muscle  and  nerve/ 

Since  analysis  shows  little  or  no  sodium  in  the 
interior  of  the  muscle  cells,  the  conclusion  follows  that 
the  essential  action  of  the  Na  ions  is  exerted  upon  the 
semi-permeable  surface  layer  or  plasma  membrane  and 
that  penetration  into  the  internal  protoplasm  is  unneces- 
sary. Overton,  however,  points  out  that  it  is  not 
necessary  to  assume  impermeability  to  these  ions  under 
all  conditions;  it  is  possible  that  under  some  conditions, 
e.g.,  stimulation,  there  may  be  an  exchange  between 
the  Na  ions  in  the  medium  and  other  cations  (e.g.,  K) 
present  in  the  muscle  cell.  This  suggests  that  impermea- 
bility to  Na  ions  is  a  characteristic  of  the  muscle  during 
the  resting  state  only,  a  view  implying  that  changes  of 
permeability  are  an  essential  factor  in  stimulation. 
Similar  views  were  expressed  by  Bernstein  and  Briinings 
at  about  the  same  time.^ 

Experiments  on  the  substitution  of  other  cations  for 
Na  showed  that  lithium  salts  were  the  only  ones  capable 
of  maintaining  irritability  in  the  same  manner  as  Na 
salts.  Pure  isotonic  solutions  of  LiCl  (0.435  P^^  cent) 
are  injurious  to  muscle,  but  a  mixture  of  this  solution 
with  an  equal  volume  of  isotonic  sugar  solution  has 
indifferent  properties  like  those  of  an  NaCl  solution. 
The  least  concentration  of  LiCl  required  for  maintaining 

^  The  cilia  of  many  marine  animals,  e.g.,  Arenicola  and  Mitykis, 
remain  active  for  hours  in  pure  solutions  of  K  and  Mg  salts. 

'  Bernstein,  Arck.  ges.  Physiol.,  XCII  (1902),  521;  Briinings,  ihid.^ 
XCVIII  (1903),  241,  and  C,  367. 


INORGANIC  SALTS  155 

irritability  is  ca  0.05  per  cent,  a  \alue  comparable  witli 
that  found  for  NaCl.  Lithium  chloride,  nitrate, 
sulphate,  phosphate,  and  acetate  all  showed  similar 
action.  All  salts  of  the  other  alkaH  cations  (XH4,  K. 
Rb,  and  Cs),  in  concentrations  equivalent  to  0.07  j)er 
cent  NaCl,  promptly  destroyed  irritability.  NaCl  solu- 
tions containing  a  Httle  K  and  Ca  (Ringer's  solution) 
were  more  effective  in  reviving  irritability  than  j)ure 
NaCl  solutions;  irritability,  however,  was  not  sustained 
by  solutions  containing  Ca  and  K  in  the  same  pr()i)or- 
tions,  but  sugar  in  place  of  NaCl.  Na  and  Ca  salts, 
especially  when  both  are  present  in  the  solution,  antago- 
nize the  toxic  action  of  potassium  salts;  this  is  readily 
shown  by  using  concentrations  of  KCl,  which,  acting 
in  pure  solution,  rapidly  destroy  irritability. 

The  addition  of  traces  of  CaCb  and  SrCb  to  isotonic 
sugar  solutions  was  found  to  delay  the  loss  of  irritability, 
and  a  slight  revival  was  observed  when  sugar-muscles 
were  returned  to  weak  solutions  of  Ca,  Sr,  Ba,  or  ^^g 
salts  in  isotonic  sugar  solution;  but  no  restorative  action 
was  observed  in  pure  isotonic  solutions  of  these  salts. 

The  results  of  experiments  with  nerve-trunks  were 
on  the  whole  similar  to  those  with  muscle,^  although  on 
account  of  the  structure  of  nerve  a  much  longer  immer- 
sion in  sugar  solution  (in  the  cold)  was  necessar)-  in 
order  to  abolish  irritabihty  completely.  The  minimal 
concentration  of  Na  salts  for  preserving  irritability 
proved  to  be  about  the  same  as  in  muscle;  on  nerve  as 
well  as  on  muscle  K  salts  have  a  characteristic  paralyzing 
action,  which  is  also  antagonized  by  Ca  and  Sr  in  the 
presence  of  Na  salts. 

*  Overton,  loc.  cit.  (1904). 


156    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

An  important  section  of  Overton's  work  has  reference 
to  the  influence  of  salts  on  the  transmission  across  the 
myoneural  junctions  and  through  reflex  arcs.  Locke^ 
(1894)  had  found  that  when  the  frog's  sartorius,  with 
nerve  attached,  was  placed  in  a  pure  isotonic  NaCl 
solution  the  tissue  within  fifteen  to  twenty  minutes 
lost  irritabihty  through  the  nerve  for  single  induction 
shocks,  while  it  remained  directly  irritable  for  some 
hours;  the  addition  of  a  little  CaClz  (0.02  per  cent)  to 
the  solution  restored  indirect  irritabihty  in  a  few  minutes; 
a  second  return  to  pure  NaCl  again  aboHshed  stimulation 
through  the  nerve,  and  the  effect  could  be  again  reversed 
by  CaCla.  Muscles  perfused  with  salt  solution  show 
the  same  phenomenon;^  and  other  cases  of  innervation, 
such  as  inhibition  of  the  heart  through  the  vagus,  are 
similarly  dependent  on  the  salts  of  the  medium.^ 

Overton^  found  that  the  addition  of  KCl  to  the  NaCl 
solution  greatly  accelerated  the  junctional  paralysis; 
salts  of  Rb  and  Cs  acted  similarly,  also  salts  of  NH3 
and  organic  ammonium  compounds,  which  have  long 
been  known  to  exhibit  this  curare-like  action.  When  the 
concentration  of  NaCl  was  0.7  per  cent,  the  addition  of 
.05  per  cent  KCl  was  found  to  shorten  the  period  of 
irritabihty  through  the  nerve  to  an  eighth  or  a  tenth 
of  its  duration  in  the  pure  solution;  with  a  lower  concen- 
tration of  NaCl  less  KC]  was  required.  This  blocking 
effect  of  potassium  is  antagonized  by  calcium;  there  is, 

^  Locke,  Zentralhl.f.  Physiol.,  VIII  (1894),  166. 

^  Gushing,  American  Journal  of  Physiology,  VI  (1901),  77. 

3  Cf.  Hober,  op.  cit.,  p.  539;  Howell,  American  Journal  of  Physiology, 
XV  (1906),  280;  Howell  and  Duke,  ibid.,  XXXV  (1907),  131. 

4  Log.  cit. 


INORGANIC  SALTS  157 

in  fact,  enough  K  in  blood  plasma  to  destroy  all  myoneural 
transmission,  were  it  not  for  the  Ca  also  present.  Cal- 
cium is  the  only  metallic  ion  in  plasma  (other  than  Na) 
required  for  myoneural  transmission;  in  mixtures  of 
NaCl  and  CaCla  indirect  irritability  is  preserved  almost 
as  long  as  in  serum.  Sr  also  antagonizes  this  action  of  K . 
but  Ba  and  Mg  do  not.  A  similar  blocking  of  myo- 
neural transmission  is  caused  by  BaCL ;  this  action  is  also 
antagonized  by  Ca.  Overton  found  that  in  a  mixed 
solution  of  sodium  and  calcium  chlorides  of  the  same 
concentration  as  in  serum  (0.7  per  cent  NaCl  plus  0.02 
to  0.03  CaCy  the  addition  of  0.05  to  0.06  per  cent  KCl 
completely  paralyzed  the  nerve-endings  without  affecting 
the  direct  irritability  of  the  muscle;  in  order  to  abolish 
the  latter  0.15  per  cent  KCl  was  required;  when  more 
CaCla  was  added  to  the  solution  more  KCl  was  required 
to  prevent  transmission.  In  the  absence  of  K  a  mere 
trace  of  Ca  is  all  that  is  necessary;  in  a  K-free  NaCl 
solution  one  part  of  CaClz  in  20,000  maintained  indirect 
irritability  for  twenty-four  hours  and  one  part  in  50,000 
for  twelve  hours;  even  one  part  in  100,000  had  a  percep- 
tible effect. 

Although  the  nerve-trunk  retains  its  power  of  conduc- 
tion for  many  hours  in  pure  solutions  of  Na  and  Li  salts, 
transmission  through  reflex  arcs  is  quickly  prevented 
by  lack  of  Ca.'  This  was  shown  both  in  perfusion 
experiments  with  intact  frogs  and  in  exi)eriments  in 
which  the  isolated  spinal  cord  with  nerves  and  muscles 
attached  was  immersed  in  the  solution.  In  such  a 
preparation  kept  at  a  low  temperature  in  well-oxygenated 

^  Overton,  Verhandl.  Ges.  deutschcr  Naturf.  u.  Arzte,  LXXV  (1903), 
Theil  II,  2te  Halfte,  p.  416. 


158    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

Ringer's  solution  reflex  activity  may  continue  for  days. 
If  the  cord  and  attached  sciatic  nerves  are  immersed 
in  isotonic  sugar  solution,  reflexes  completely  disappear 
within  twenty-four  to  thirty-six  hours;  on  returning  the 
cord  to  Ringer's  solution  they  return  in  a  few  hours. 
In  perfused  frogs,  replacement  of  the  blood  by  sugar 
solution  rapidly  causes  disappearance  of  reflexes  and 
later  of  direct  muscular  irritability:  perfusion  with  pure 
NaCl  solution  then  restores  direct  muscular  irritability, 
but  not  indirect  or  reflex,  while  Ringer's  solution  restores 
all  three.  The  quantity  of  Ca  necessary  for  restoring 
reflexes  (as  well  as  indirect  irritability)  is  very  shght. 

In  the  observations  above  most  of  the  fundamental 
phenomena  of  salt  action  are  illustrated — the  necessity  of 
salts  for  cellular  activity,  the  toxic  action  of  pure  solu- 
tions, ion-antagonisms,  and  especially  the  remarkable 
role  of  calcium  in  maintaining  the  normal  structural 
and  functional  relationships  between  cells.  With  regard 
to  this  latter  phenomenon,  Overton  cites  Herbst's 
observations  on  the  action  of  calcium  in  promoting  the 
coherence  of  blastomeres,^  and  also  calls  attention  to  the 
presence  of  this  element  in  the  middle  lamella  of  plant 
tissues,  where,  according  to  Mangin,  it  is  present  as  a 
compound,  Ca-pectate  (or  pectinate),  which  is  necessary 
for  intercellular  coherence.  When  this  compound  is 
removed  (by  weak  acid)  or  when  it  is  substituted  by  the 
Na  salt  (e.g.,  in  pure  NaCl  solution)  the  cells  fall  apart.^ 
Apparently   some   Ca   compound  is  necessary   for   the 

'  Herbst,  Arch.  Entwicklungsmech.,  IX  (1900),  424. 

2  Compare  the  recent  observations  of  Hansteen  on  plant  tissues; 
again  pure  NaCl  solutions  cause  a  disintegration  due  to  loss  of  intercellular 
coherence:  Jahrb.  wiss.  Botanik,  XLVII  (1910),  289;  LIII  (1914),  536. 


INORGANIC  SALTS  159 

intimate  union  between  the  nerve  end-plate  and  muscle 
cell,  or  for  the  normal  properties  of  the  synaptic  junc- 
tions. Overton  suggests  that  when  the  tissue  is  trans- 
ferred to  pure  NaCl  solution,  the  Ca  in  this  compound 
is  replaced  by  Na,  producing  a  compound  of  greater 
water-absorbing  properties,  which  swells  and  interrujns 
the  union.  Such  an  effect  is  reversed  by  a  return  to 
Ca-containing  solutions. 

Some  of  the  more  general  inferences  to  be  drawn  from 
these  and  recent  experiments  of  a  similar  kind  are  as 
follows:  Since  irritabiUty  disappears  in  isotonic  sugar 
solutions,  which  maintain  the  osmotic  balance  without 
apparently  changing  the  crystalloid  content  of  the  cell, 
it  seems  clear  that  the  action  of  the  salts  of  the  external 
medium  must  be  superficial;  i.e.,  is  a  surface-action 
exerted  upon  the  plasma  membrane.  This  action  is 
probably  of  a  twofold  nature:  first,  the  normal  composi- 
tion and  physical  properties  of  the  colloidal  materials 
composing  the  surface-film  are  preserved  only  when  a 
certain  combination  of  ions  is  present  in  the  medium; 
and,  second,  the  normal  state  of  electrical  polarization  of 
the  membrane  is  also  dependent  on  the  presence  of  salts 
in  the  medium  as  well  as  in  the  cell-interior;  this  effect 
is  important  because  the  electrical  polarization  of  the 
membrane  is  a  factor  determining  its  permeability. 
These  two  effects,  however,  cannot  be  regarded  as 
independent,  since  changes  in  the  physical  state  of  the 
membrane  must  alter  its  permeability  and  (in  so  doing) 
its  electrical  polarization;  and,  conversely,  changing  the 
electrical  polarization  influences  the  permeability. 

The  essential  conclusion,  however,  is  that  salts  may 
exert  physiological  action  without  penetrating  into  the 


i6o    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

interior  of  the  cell,  solely  by  altering  the  state  of  the 
plasma  membrane,  and  there  is  much  additional  evidence 
that  this  is  the  case.  The  analytical  results  of  Urano 
and  Fahr^  show  that  in  normal  vertebrate  muscle  Na 
is  almost  entirely  absent  from  the  cell  interior,  although, 
as  just  shown,  it  is  essential  to  the  maintenance  of  irrita- 
bility. Urano  kept  frogs'  sartorii  for  several  hours  in 
isotonic  sugar  solution,  and  found  that  the  muscle  gave 
off  to  the  solution  relatively  much  more  Na  than  K. 
Muscles  thoroughly  extracted  in  sugar  solution  were  found 
to  contain  only  2  per  cent  or  less  of  the  normal  total  Na- 
content,  but  nearly  all  of  the  K  and  phosphate.  The 
conclusion  seems  certain  that  the  Na  is  contained  almost 
entirely  in  the  intercellular  spaces  of  the  tissue,  and  the 
K  and  phosphate  in  the  cells.  Muscles  kept  for  six 
hours  in  sugar  solution  lose  very  little  ash  that  may  not 
be  accounted  for  by  the  salts  present  in  the  interstitial 
lymph.  Fahr,  in  an  ash-analysis  of  the  extract  of  fresh 
uninjured  muscles  in  isotonic  sugar  solution,  found  that 
only  6  per  cent  of  the  original  K  of  the  tissue,  but  90 
per  cent  of  the  original  Na,  was  thus  recoverable.  If 
four-fifths  of  the  total  volume  of  the  muscle  be  regarded 
as  consisting  of  muscle  cells,  and  one-fifth  of  interstitial 
tissue  and  lymph  spaces,  the  Na-content  of  the  tissue 
is  completely  accounted  for  by  the  salts  present  in  the 
lymph.  The  latter  must  therefore  exert  their  physio- 
logical influence  through  their  action  upon  the  external 
protoplasmic  layer  or  plasma  membrane. 

Hober's  experiments  on  the  influence  of  isotonic 
solutions  of  neutral  salts  on  the  demarcation-current 
potential  of  muscle^  also  support  Overton's  view  that 

^  Loc.  cit.        *  Hober,  Arch,  ges.  Physiol.,  CVI  (1905),  599. 


INORGANIC  SALTS  i6i 

the  normal  uninjured  resting  muscle  is  impermeable  to 
sodium  salts.  Solutions  of  sodium  and  lithium  salts 
leave  the  normal  electrical  potential  of  the  external 
muscle-surface  unchanged;  while  salts  like  those  of  K, 
Rb  and  NH4  (which  give  other  evidence  of  penetrating 
the  muscle)  produce  an  injury-current  or  local  negativity. 
Absence  of  penetration  is  indicated  by  failure  to  change 
the  external  potential  of  the  muscle;  the  alkali  earth 
salts  and  in  part  those  of  caesium  are  thus  indifferent. 
Nevertheless,  they  alter  the  properties  of  the  tissue; 
thus  Mg  salts  have  a  strongly  anti-stimulating  or  narcotic 
action,  and  Ca  and  Sr  salts  in  pure  isotonic  solution 
similarly  render  muscle  resistant  to  stimulation;  all  of 
these  effects  are  reversible  if  the  exposures  are  not  too 
prolonged. 

Loss  of  contractility  in  non-electrolyte  solutions  and 
its  prompt  return  in  solutions  of  sodium  salts — especially 
if  some  Ca  is  also  present— are  characteristic  of  many 
varieties  of  muscle.  Among  invertebrates  the  larva?  of 
Arenicola  show  this  phenomenon  in  a  striking  manner;' 
here  also,  as  with  vertebrate  muscle,  Li  and  Na  salts  are 
alone  capable  of  preserving  contractility  for  prolonged 
periods,  and  K  salts  have  a  paralyzing  action.  Mg 
salts  repress  contractility  very  promptly  and  comj^letely. 
and  the  action  is  readily  reversed,  especially  by  solutions 
of  Na  salts  containing  a  Httle  Ca.^  The  resemblance  of 
Li  to  Na  in  its  power  of  maintaining  the  normal  properties 
of  muscle  (though  less  perfectly  than  Na)  seems  to  be 
general  for  both  vertebrate  and  invertebrate  muscle; 
for  example.  Mines  describes  this  phenomenon  in  the 

'  R.  S.  Lillie,  American  Journal  of  Physiology,  XXI\'  (1909),  459- 
2  Op.  cit.,  p.  485. 


i62    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

moUuscan  heart  {PedenY  and  in  the  heart  of  elasmo- 
branch  fishes. 

Much  further  evidence  could  be  cited  indicating  that 
changes  in  the  plasma  membranes  of  the  hving  cells, 
produced  by  salts  or  other  compounds  which  show  no 
evidence  of  penetrating  into  the  cell  interior,  may 
profoundly  affect  the  properties  of  irritable  tissues  or 
organisms.  An  interesting  example  is  seen  in  the 
changes  produced  by  isotonic  salt  solutions  in  the 
sensiti\aty  of  frog's  muscle  to  various  forms  of  chemical 
stimuH  and  to  physical  agents  like  heat  or  contact. 
A  curarized  frog's  gastrocnemius,  placed  for  a  few 
minutes  in  a  pure  isotonic  solution  of  a  sodium  salt 
(NaCl,  NaBr,  NaNO^,  Nal,  NaC103,  etc.)  and  then 
dipped  into  a  solution  containing  a  stimulating  compound 
(K  salt)  or  a  cytolytic  agent  (chloroform  in  saturated 
solution),  contracts  much  more  vigorously  than  a 
normal  muscle  which  is  dipped  into  the  same  solution 
directly  from  Ringer's  solution.  The  pure  Na  salt 
solution  increases  the  responsiveness  to  the  stimulating 
agent;  i.e.,  induces  a  sensitization;  this  effect  is  readily 
antagonized  by  CaCla.  The  reverse  effect  (desensitiza- 
tion)  is  produced  by  exposure  to  isotonic  CaCla,  SrCla, 
or  MgCla ;  after  a  brief  stay  in  these  solutions  the  muscle 
fails  to  respond  to  the  stimulating  solution  or  responds 
subnormally.  In  all  such  cases  normal  irritabiUty 
returns  in  Ringer's  solution.^  Various  facts  indicate 
that  Ca  compounds  in  the  surface  layer  of  the  cell  are 

^  G.  R.  Mines,  Journal  of  Physiology,  XLIII  (191 2),  467. 

*  R.  S.  LUlie,  Proceedings  of  the  Society  of  Experimental  Biology  and 
Medicine,  VI  (19 10),  170;  American  Journal  of  Physiology,  XXVIII 
(1911),  197;  cf.  p.  215. 


INORGANIC  SALTS  163 

concerned  in  normal  irritability;'  a  striking  examj)lc  is 
the  marked  hypersensitivity  induced  in  frog's  muscle 
and  nerve  by  Na  salts  whose  anions  precipitate  calcium 
or  form  Ca  salts  of  limited  solubility.  Muscles  treated 
for  a  few  minutes  with  isotonic  solutions  of  these  salts 
(sulphate,  phosphate,  tartrate,  citrate,  oxalate,  etc.) 
become  highly  sensitive  to  the  contact  of  foreign  sub- 
stances or  media,  and  contract  vigorously  when  exposed 
to  air.^  These  phenomena  of  sensitization  are  produced 
so  rapidly  as  to  leave  little  doubt  that  they  depend  on 
alterations  in  the  surface-films  of  the  cells. ^ 

Direct  evidence  that  changes  in  the  permeability  of 
the  plasma  membranes  play  an  essential  part  in  processes 
of  stimulation  will  be  cited  later.  Apparently  all 
substances  that  alter  the  physical  or  chemical  state  of 
the  plasma  membrane  (salts,  acids,  alkalis,  narcotic 
agents)  modify  the  stimulation-process;  this  influence 
may  be  in  the  direction  either  of  facilitation  or  of  repres- 
sion, according  to  conditions."* 

The  precise  means  by  which  salts  produce  these 
effects  has  been  much  debated  and  is  still  imperfectly 

^  Cf.  the  experiments  of  A.  J.  Clark,  cited  on  page  185. 

2  J.  Loeb,  American  Journal  of  Physiology,  V  (190 1),  362. 

3  Other  effects  dependent  on  surface  changes  in  the  cells  are  related 
to  those  just  described;  e.g.,  changes  in  the  surface-films  of  blood 
corpuscles  and  bacteria,  affecting  the  critical  concentrations  of  hemolysis 
or  agglutination  by  H  ions,  are  produced  by  the  addition  of  proteins; 
cf.  the  recent  papers  of  Coulter,  Jour.  Gen.  Physiol.,  Ill  (1921),  3091  and 
IV  (1922),  403;  Northrop  and  De  Kruif,  ibid.,  IV  (1922),  655;  also 
Eggerth  and  Bellows,  ibid.,  p.  669. 

4  Such  effects  evidently  imply  an  influence  on  cell  metabolism. 
Warburg's  observations  on  sea-urchin  eggs  show  that  the  oxygen  con- 
sumption may  be  increased  several  times  by  the  addition  of  alkali  which 
shows  no  evidence  of  penetrating  the  cell:  Z.  physiol.  Chcm.,  LX\T 
(1910),  305. 


1 64    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

understood.  Perhaps  the  clearest  light  on  the  problem 
has  been  afforded  by  the  phenomena  of  salt-antagonism. 
These  have  shown  definitely,  at  least  in  certain  cases, 
that  structural  changes  in  those  parts  of  the  cell  which 
are  most  directly  exposed  to  the  action  of  the  solution 
(plasma  membranes  and  other  surface-structures  like 
cilia)  are  the  primary  condition  of  the  effects  produced. 
The  toxic  and  other  effects  are  secondary  consequences 
of  these  structural  changes.  The  physical  condition  of 
the  structural  colloids — state  of  subdivision,  of  hydration, 
of  electrical  polarization,  etc. — is  changed  by  the  action 
of  the  salt,  with  corresponding  changes  in  the  properties 
of  the  cell-structure  itself  and  of  the  chemical  and  other 
activities  controlled  by  it.  In  many  cases  the  injurious 
action  of  the  pure  salt-solution  (NaCl)  is  referable  to  a 
destruction  of  the  normal  semi-permeabiHty  of  the  plasma 
membrane;  this  effect,  if  not  soon  reversed,  involves 
chemical  and  other  disorganization  followed  by  death. 
Any  condition  preventing  or  retarding  the  alterative 
action  on  the  membrane,  such  as  the  presence  of  an 
antagonistic  salt  or  non- electrolyte  (narcotic),  has 
accordingly  a  protective  or  "anti-toxic"  action.^  These 
general  conditions  are  well  illustrated  in  a  simple  marine 
organism  much  used  in  experimental  work  at  Woods 
Hole,  the  larva  of  the  annelid  Arenicola  cristata.  This 
is  a  segmented  trochophore  larva  about  one-third  of 
a  mihimeter  in  length,  having  pigmented  body  cells 
and  swimming  by  a  combination  of  muscular  and 
ciliary    movements.     When    placed    in    pure    isotonic 

'  Cf.  the  discussion  in  my  paper  on  antagonism  between  salts  and 
anaesthetics,  American  Journal  of  Physiology,  XXXI  (1913),  255;  cf. 
pp.  2  75ff. 


INORGANIC  SALTS  165 

NaCl  (or  similar  unbalanced  solution  of  alkali  salt; 
the  larvae  contract  strongly  and  the  yellow  pi^qnent 
begins  to  diffuse  from  the  cells;  by  degrees  the  cilia 
cease  movement  and  undergo  a  visible  breakdown  or 
disintegration  (suggesting  liquefaction  or  absorption  (jf 
water).  In  a  solution  of  NaCl  containing  a  little 
CaCla  (95  volume  m/2  NaCl  plus  5  vols,  m/2  CaCb)  all 
of  these  immediate  effects  are  prevented,  and  the  larva; 
retain  their  normal  appearance  and  behavior  for  some 
time  and  die  much  more  gradually.^ 

In  this  case  it  is  clear  that  the  iimnediate  action  of 
the  pure  salt-solution  is  upon  the  surface  structures — 
cilia  and  plasma  membranes — which  quickly  lose  their 
normal  structural  coherence  and  continuity;  the  result 
of  this  change  in  the  ciha  is  physical  breakdown,  and 
in  the  plasma  membrane  a  marked  increase  of  permea- 
bility, hence  the  diffusion  of  soluble  cell-constituents  to 
the  exterior  and  the  progressive  disorganization.  In 
many  other  organisms  and  cells  it  can  also  be  shown  that 
an  abnormal  increase  of  permeability  is  produced  by 
pure  solutions  of  Na  salts  and  prevented  by  the  addition 
of  CaCla  or  other  antagonistic  salt."^  The  exj^eriments  of 
Osterhout  on  the  electrical  conductivity  of  Lamina ria 
and  other  plant  tissues  afford  perhaps  the  clearest  evi- 
dence that  the  toxic  action  of  pure  NaCl  solutions  is  the 
result  of  a  destruction  of  semi-permeabiUty  and  that 
antagonistic  salts  (CaCL  and  others)  produce  their  anti- 

^  American  Journal  of  Physiology,  XXIV  (1909),  14;  cf.  pages  22  iT. 

2  In  an  earlier  paper  {Biological  Bulletin,  XVII  [igog],  188)  I  have 
given  a  summary  of  observations  showing  tlie  correlation  between 
permeability-increasing  action  and  toxicity  for  compounds  oUicr  than 
salts. 


1 66    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

toxic  effects  by  counteracting  the  structural  change  in 
the  membrane.^ 

The  question  of  just  how,  in  the  physico-chemical 
sense  this  result  is  accomplished  is  a  fundamental  one; 
salt  antagonism  is  shown  by  all  groups  of  organisms  from 
bacteria^  to  vertebrata,  and  is  apparently  a  universal 
phenomenon  in  living  protoplasm.  It  should  be  noted 
that  other  effects  produced  by  the  pure  Na  salt  solu- 
tion are  also  antagonized  by  Ca  and  other  salts;  e.g.,  its 
stimulating  action,  shown  in  the  production  of  twitches 
in  vertebrate  and  other  muscle,^  the  sensitizing  action 
on  muscle  just  described,  and  the  activation  of  unfertil- 
ized eggs."*  The  fact  that  prevention  (by  Ca  and  nar- 
cotics) of  increase  of  permeability  in  various  irritable 
tissues  and  organisms  is  associated  with  prevention  of 
stimulation  has  a  general  interest  as  evidence  of  the 
essential  part  played  by  membranes  in  stimulation,  and 
will  be  considered  more  fully  later. 

The  problem  of  the  physico-chemical  basis  of  salt 
antagonism  has  been  approached  in  various  ways  and 

^  Osterhout,  loc.  cit.  Related  observations  are  those  of  Ham- 
burger on  the  action  of  calcium  in  preventing  the  increase  in  perme- 
ability produced  in  frog's  kidneys  perfused  by  NaCl  solutions  containing 
dextrose  (cf.  Hamburger,  Biochem.  Zeitschrift,  LXXXVIII  [1918],  97). 
In  1904  J.  B.  MacCallum  had  observed  the  antidiuretic  action  of  calcium 
salts  and  had  related  it  to  the  action  in  decreasing  permeability  (Journal 
of  Experimental  Zoology,  I  [1904J,  179;  University  of  California  Pub- 
lications, Physiol.,  II  [1905],  93).  It  is  weU  known  that  calcium  antago- 
nizes cytolysis  by  saponin  and  other  permeability-increasing  compounds. 
Chiari's  observations  on  the  formation  of  exudates  and  many  other  obser- 
vations are  related;   cf.  Hober,  op.  cit.,  pp.  544  £F. 

*  For  the  case  of  bacteria  cf.  Shearer,  Journal  of  Hygiene,  XVIII 
(1919),  339- 

3  Cf .  Loeb's  article  in  Festschrift  fur  Fick,  loc.  cit. 

4  R.  S.  LilHe,  American  Journal  of  Physiology,  XXVII  (1911),  289; 
Journal  of  Morphology,  XXII  (191 1),  695. 


INORGANIC  SALTS  167 

on  the  whole  most  effectively  by  comparing;  the  action  of 
salts  on  colloidal  solutions  and  emulsions  with  their 
action  on  living  cells.^  The  physiological  effects  i)ro- 
duced  by  salts  and  salt  combinations  vary  with  the  nature 
of  the  ions  in  a  manner  which  in  many  cases  shows  a 
close  parallelism  with  the  physical  effects  produced  by 
the  same  salts  in  simple  colloidal  systems.  For  example, 
in  the  counteraction  of  the  toxic  effects  of  pure  Xa  salt 
solutions  the  results  all  indicate  that  the  cation  of  the 
antagonistic  salt  is  the  effective  agent;  and  in  this  case 
certain  relations  highly  characteristic  of  the  action  of 
ions  on  colloidal  systems  are  shown  clearly;  thus  with 
the  cilia  of  Arenicola  all  salts  of  bivalent  hea\y  metals 
(Co,  Ni,  Cd,  Zn,  Mn,  Pb,  Fe++,  Cu)  were  found  to  pro- 
duce their  maximal  antitoxic  effects  in  concentrations  of 
the  order  m/400  to  m/i6oo;  while  with  trivalent  metals 
(Al,  Cr,  Yt'")  the  physiologically  corresponding  concen- 
trations were  from  50  to  100  times  less.^  This  increase 
in  effectiveness  with  increase  in  valence  is  characteristic 
of  the  action  of  salts  on  negatively  charged  suspensoid 
systems  (rule  of  Schulze  and  Hardy);  and  aj:)parently 
the  observations  above  indicate  that  the  cations  produce 
their  effects  in  the  living  system  by  influencing  the  state 
of  subdivision  of  the  suspensoid  colloids  forming  part 
of  the  protoplasmic  structure.  Other  cases  of  rapid 
increase  in  physiological  effectiveness  with  increase  of 
valence  are  well  known. 

Such  cases  of  antagonism  are  consistent  with  the  hy- 
pothesis that  the  normal  state  of  the  living  i^rotoplasmic 

I  Cf.  Hober's  review  in  his  textbook,  chap,  x,  p.  47i- 
^American  Journal  of  Physiology,  VII  (1904),  419;    similar  results 
were  obtained  with  the  gill  cilia  of  Milylus:  ibid.,  X\'II  (igo^O,  Sy. 


1 68  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

structure  (e.g.,  a  cilium  or  plasma  membrane)  requires  a 
certain  state  of  subdivision  of  the  chief  structural  colloids. 
Apparently  in  the  normal  medium,  e.g.,  sea  water,  the 
influence  of  the  various  ions  is  so  balanced  as  to  preserve 
this  state;  the  collective  effect  of  the  negative  charges 
carried  by  the  anions  (CI,  SO4,  HCO3,  ^tc.)  is  just 
balanced  by  the  collective  effect  of  the  positive  charges 
carried  by  the  cations  (Na,  K,  Ca,  Mg).  In  the  pure 
solution,  however,  of  NaCl,  in  which  no  bivalent  cations 
are  present,  the  influence  of  the  anions  is  insufflciently 
compensated,  and  the  colloids  are  altered  in  a  manner 
injurious  to  cell  structure:  i.e.,  a  preponderant  influence 
of  anions  is  the  essential  toxic  factor  in  such  cases.  The 
addition  of  bivalent  or  trivalent  cations  of  any  kind 
has  under  these  conditions  a  compensating  and  hence 
antagonistic  or  antitoxic  influence;  trivalent  ions  exercise 
this  effect  in  much  lower  dilution  than  bivalent  ions, 
and  bivalent  than  monovalent  ions.  At  an  appropriate 
concentration,  the  balance  is  restored,  protoplasmic 
structure  remains  normal,  and  life  continues.  The 
reverse  condition,  in  which  the  toxic  action  of  the  pure 
solution  results  from  a  prepotency  of  cation  action,  and 
in  which  accordingly  the  addition  of  small  quantities  of 
salts  with  powerfully  acting  anions  has  an  antitoxic 
effect,  is  apparently  also  realized  in  some  cases;  e.g.,  the 
ciliated  epithelium  of  the  molluscan  gill  {Mitylus)  in  solu- 
tions of  SrCla;  here  various  Na  salts  (NaOH,  NaBr,  Nal, 
NaCNS,  NaaSOJ  show  well-marked  antagonistic  action.^ 
Such  purely  physical  explanations,  while  apparently 
partly  applicable  in  some  cases,   prove  inadequate  in 

^  Cf.  American  Journal  of  Physiology,  XVII  (1906),  89;  cf.  p.  129; 
cf.  Raber,  Jour.  Gen.  Physiol.,  II  (1920),  541,  for  analogous  observations 
on  Lamitiaria. 


INORGANIC  SALTS  169 

many  others,  where  the  foregoing  relation  of  antagonism 
to  valence  does  not  appear  to  hold,  and  especially  in 
those  numerous  cases  where  different  cations  similar  in 
valence  have  widely  different  antagonistic  or  other 
physiological  actions.'  In  such  cases  the  special  chemical 
properties  of  the  compounds  formed  between  the  ions 
and  the  structural  colloids  of  the  cell  must  apparently 
be  taken  into  consideration.  Thus  various  facts  indicate 
that  calcium  proteinates  or  calcium  soaps  (or  both) 
are  of  special  importance  as  constituents  of  cell  structures; 
and  these  compounds  cannot  be  replaced  satisfactorily 
by  the  corresponding  compounds  of  other  bivalent 
elements.^  Such  a  conception  explains  why  strontium, 
the  metal  most  closely  resembling  calcium  in  general 
chemical  properties,  usually  comes  nearest  to  calcium  in 
antagonistic  effectiveness;  the  other  alkali  earth  cations 
come  next;  while  the  bivalent  heavy  metals  are  effect- 
ive in  only  a  few  special  cases  (Mn.  Co,  Fe++),  the  great 
majority  of  these  metals  being  too  strongly  toxic  to  act 
as  efficient  antagonists.^ 

^  Cf.  Hober's  discussion  in  his  recent  papers  on  the  physiological 
action  of  calcium;  Arch.  ges.  Physiol.,  CLXVI  (191  ?)»  53 1>  ^^^^ 
CLXXXII  (1920),  104. 

2  The  cases  are  numerous  where  calcium  has  a  specitk  action  which 
cannot  be  replaced  by  that  of  other  cations,  even  Sr;  instances  are  tlie 
specificity  of  calcium  in  phagocytosis  (Hamburger),  in  the  inhibition 
of  swimming  plates,  and  in  the  preservation  of  contractiHty  in  heart- 
strips.  On  the  other  hand,  in  its  simple  stabilizing  or  protective  action, 
(e.g.,  in  cytolysis,  etc.)  Ca  can  often  be  replaced  by  other  cations  (cf. 
Hober's  papers,  loc.  ciL;  cf.  also  Wiechmann,  Arch.  gcs.  Physiol.,  CXC\ 
[1922],  588). 

3  Nevertheless  even  the  most  toxic  cations,  Hke  Ag  and  Hg,  may 
show  definite  antitoxic  action  in  certain  cases;  e.g.,  the  beat  of  the 
ctenophore  swimming  plate  in  pure  isotonic  NaCl  sohition  is  prolonged 
several  times  by  AgNOj  and  HgCh  in  concentrations  of  m/ 100,000  to 
m/200,000  (cf.  American  Journal  of  Physiology,  X\'I  [190^^!.  "/)• 


lyo    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

The  evidence,  taken  as  a  whole,  indicates  that  the 
salts  act  chiefly  by  altering  the  physical  state  of  the 
structural  colloids  of  the  cell;  and  it  is  to  be  presumed 
that  general  physical  factors  (of  the  kind  regarded  as 
acting  in  all  colloidal  phenomena)  and  special  chemical 
factors  specific  for  each  form  of  protoplasm  are  both 
concerned  in  producing  the  total  effect.  In  the  directly 
toxic  or  injurious  action  of  salt  solutions,  a  frequent,  if 
not  invariable,  factor  is  a  destruction  of  the  semi- 
permeable properties  of  the  protoplasmic  partitions, 
primarily  of  the  plasma  membranes.  In  physiological 
salt-actions  of  other  kinds,  e.g.,  stimulation,  sensitization, 
inhibition,  it  is  to  be  presumed  that  the  physical  proper- 
ties of  the  plasma  membranes  undergo  special  modifica- 
tions of  a  corresponding  kind,  but  that  the  effects  do  not 
exceed  a  certain  range  and  are  therefore  reversible. 
The  general  fact  that  a  certain  combination  of  salts, 
usually  of  Na,  Ca,  and  K,  is  required  in  the  external 
medium  for  most  forms  of  normal  protoplasmic  action 
indicates  the  fundamental  importance  of  the  influence 
of  salts  on  the  structural  colloids  of  protoplasm.  Appar- 
ently the  structural  conditions  required  for  the  continuity 
and  closeness  of  texture  necessary  in  semi-permeable 
membranes  depend  on  the  maintenance  of  a  definite 
equihbrium  between  the  ions  in  the  medium  and  those 
associated  (chemicaUy  or  otherwise)  with  the  structural 
coUoids.  SKght  changes  in  the  salt-content  imply 
corresponding  structural  changes,  with  dependent  physio- 
logical effects. 

It  should  be  added  that  other  general  physical 
conditions,  also  dependent  on  the  presence  of  salts, 
are  of  importance  in  the  normal  activity  of  protoplasm, 


INORGANIC  SALTS 


171 


such  as  the  electrical  conductivity  of  proto])hism  and 
medium  and  the  electrical  polarization  of  the  plasma 
membranes.  These  conditions  will  be  considered  later 
under  the  subject  of  stimulation. 

The  special  relations  of  the  three  chief  cations  of 
the  protoplasmic  media,  Na,  K,  and  Ca,  to  protoplasmic 
activity  appear  to  depend  on  chemical  conditions  of  a 
kind  still  imperfectly  understood.  The  differences 
between  the  physiological  actions  of  Na  (and  Li)  and  of  K 
(and  Rb  and  Cs)  in  their  relation  to  vertebrate  muscle 
and  nerve  cannot  be  satisfactorily  explained  on  the  basis 
of  the  physico-chemical  constants  of  these  ions.  Na 
and  K,  though  chemically  closely  similar,  appear  in 
many  forms  of  protoplasm,  e.g.,  vertebrate  muscle,  to 
act  as  physiological  antagonists;  in  others  their  physio- 
logical differences  are  relatively  sHght;  e.g.,  in  the  case 
of  fish  eggs  (Fundulus)  and  sea-urchin  eggs  (Arbacia) 
isotonic  KCl  solution  is  even  less  toxic  than  NaCl  solu- 
tion;  both  solutions  are  antagonized  by  Ca. 

It  is  remarkable  that  the  striated  muscle  cells  of 
vertebrata  appear  to  be  readily  permeable  to  some  K 
salts  (KCl,  KBr,  KI,  KNO3)  but  not  to  others  (K,SO„ 
K-tartrate,  K-phosphate) ;'  in  this  respect  K  salts 
exhibit  a  striking  contrast  to  Na  salts.  The  special 
permeabihty  to  KCl  is  shown  in  frog's  muscle  by  rai)i(l 
increase  in  the  weight  of  the  tissue  when  it  is  immersed 
in  isotonic  solutions  of  this  salt;  similar  conditions  have 
been  found  by  Seebeck'  in  the  frog's  kidney,  which,  like 
muscle,  shows  normal  semi-permeal^ility  toward  Na  and 
Li  salts.     The  special  physiological  action  of  K  is  prob- 

^  Overton,  Arch.  ges.  Physiol.,  CV  (1904),  176. 
=>  Seebeck,  ibid.,  CXLVIII  (1912),  443- 


172    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

ably  related  to  this  peculiarity,  but  the  nature  of  the 
relationship  is  unknown.  Recently  Zwaardemaker  has 
attributed  importance  to  the  sHght  radioactivity  of  K, 
on  the  ground  of  certain  striking  parallels  between  the 
action  of  K  salts  and  uranium  salts  on  the  frog's  heart  ;^ 
but  other  evidence  from  experiments  with  marine 
organisms  fails  to  support  this  view.^ 

Recently  Meigs^  has  investigated  the  osmotic  behavior 
of  smooth  muscle  in  solutions  of  salts  and  non-electro- 
lytes, and  finds  a  number  of  remarkable  differences 
between  this  tissue  and  striated  muscle.  For  example, 
the  stomach  muscle  of-  the  frog  gains  weight  when 
immersed  in  isotonic  solutions  of  sugar,  alanin,  or 
NaCl,  and  even  in  Ringer's  solution.  He  concludes 
that  smooth  muscle  cells  differ  fundamentally  in  their 
structure  and  mode  of  action  from  striated  muscle  cells, 
and  that  they  are  not  surrounded  by  semi-permeable 
membranes.  In  the  adductor  muscle  of  the  marine  clam 
(Venus  mercenaria) ,  a  smooth  muscle  which  reacts 
slowly  and  maintains  its  state  of  tension  for  a  long  time, 
closely  similar  conditions  were  found.  Pieces  of  muscle 
inamersed  in  sea  water  take  up  chloride  from  the  latter 
and  increase  in  weight;  they  even  fail  to  lose  weight  in 
lo  per  cent  NaCl  or  in  sea  water  of  twice  the  normal 
concentration."^ 

^  Zwaardemaker,  Journal  of  Physiology,  LIII  (1920),  273,  and 
LV  (1921),  ss- 

2  R.  F.  Loeb,  Journal  of  General  Physiology,  III  (1920),  229.  A.  J. 
Clark  fails  to  confirm  Zwaardemaker's  claim  that  uranium  can  act 
as  a  substitute  for  K  in  restoring  the  heartbeat  (Journal  of  Pharmacology 
and  Experimental  Therapeutics,  XVIII  [1922],  423). 

3  E.  B.  Meigs,  Journal  of  Experimental  Zoology,  XIII  (191 2),  497. 
''Meigs,  Journal  of  Biological  Chemistry,  XVII  (1914),  81. 


INORGANIC  SALTS  173 

In  explanation  of  these  apparent  discrepancies  it 
has  been  suggested  that  smooth  muscle  cells  are  easily 
injured  and  that  the  normal  semi-permeability  had  dis- 
appeared at  the  time  when  the  tissue  was  examined,  but 
this  possibihty  is  rejected  by  Meigs.  It  is  dilTicult  to 
escape  the  conclusion  that  a  continuous  semi-permeable 
membrane  does  not  invest  the  whole  cellular  element  in 
this  tissue.  Possibly  the  contractile  part  of  the  entire 
structure  has  a  relation  to  the  protoplasmic  part  similar 
to  that  which  the  fibers  in  connective  tissue  have  to  the 
cells  by  which  they  are  formed.  The  sluggishness  of 
the  movement  and  its  slow  reversibility  suggest  a 
fundamentally  different  type  of  organization  froni 
that  of  striated  muscle  cells.  Semi-permeability  appears 
to  be  universal  in  indifferentiated  cellular  elements  and 
in  the  majority  of  specialized  cells;  but  a  differentiation 
in  which  part  of  the  total  structure  acquires  non-cellular 
properties  is  not  infrequent  in  organisms,  as  illustrated 
in  connective  tissues  and  skeletal  structures;  and  the 
above-cited  types  of  contractile  tissue  may  exemplify 
this  general  condition. 

The  penetration  of  salts  through  the  egg-membrane 
of  the  sea-minnow,  Fundulus,  as  shown  in  various  toxic 
effects  and  antagonisms,  illustrates  many  conditions  of 
great  interest,  and  especially  indicates  the  importance 
of  the  purely  chemical  factors  in  permeability.  This 
membrane  is  a  dead  structure,  or  chorion,  external  to 
the  living  protoplasm  of  the  Qgg,  and  apparently  consist- 
ing chiefly  of  a  keratin-like  protein.  In  its  normal 
state,  it  is  almost  completely  impermeable  to  water  or 
the  salts  of  the  medium;  hence  the  eggs  will  develop 
either  in  distilled  water  or  in  concentrated  sea  water. 


174    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

Pure  salt  solutions  (NaCl)  or  solutions  of  acid  or  alkali 
alter  the  membrane  and  allow  penetration.  Character- 
istic antagonisms  are  shown  in  these  effects;^  e.g.,  the 
penetration  of  heavy  metal  salts  (cobalt  and  nickel)  is 
retarded  by  CaClz  and  their  toxic  action  is  thus  pre- 
vented.^ Eggs  placed  in  pure  strongly  hypertonic 
NaCl  solutions  float  at  first,  but  soon  sink  and  die, 
indicating  the  penetration  of  salt  and  water  as  the 
membrane  is  altered;  but  in  the  same  solution  to  which 
CaCla  has  been  added,  they  may  float  and  remain 
living  for  several  days.^  Recently  Loeb  and  Cattell  have 
studied  the  penetration  of  K  salts  and  acids  into  the 
Fundulus  egg  in  the  presence  of  other  salts  (alkali  and 
alkah  earth)  in  varying  concentrations."*  As  index  of 
the  penetration  of  KCl  the  paralyzing  action  of  the  salt 
on  the  heart  was  used;  this  action  is  reversible,  so  that 
if  eggs  containing  embryos  whose  hearts  have  previously 
been  arrested  in  KCl  solution  are  placed  in  sea  water,  the 
heartbeat  after  a  time  revives,  indicating  outward 
dift'usion  of  KCl  through  the  membrane.  The  remark- 
able fact  is  that  this  recovery  does  not  occur  in  distilled 
water  or  in  solutions  of  non-electrolytes;  in  order  that 
the  potassium  shall  penetrate  the  membrane,  a  treatment 
of  the  latter  with  salt  solutions  is  necessary.  Thus 
(typically)  all  of  the  poisoned  hearts  resume  beating 
within  a  day  when  the  eggs  are  placed  in  sea  water  or 

'  Cf.  the  article  by  J.  Loeb  in  Oppenheimer's  Handhuch  der  Bio- 
chemie,  II,  104,  for  a  general  account  of  antagonisms  in  Fundulus  eggs. 

'A.  P.  Mathews,  American  Journal  of  Physiology,  XII  (1905),  419. 

3  Loeb,  Science,  XXXVI  (1912),  637;    Biochem.  Zeitschrijt,  XL VII 
(1912),  127. 

4  Loeb  and  Cattell,  Journal  of  Biological  Chemistry,  XXIII  (1915), 
41;  Loeb,  ibid.,  XXVII  (1916),  339,  352,  363;  XXVIII,  175. 


INORGANIC  SALTS  175 

isotonic  NaCl  solutions,  while  none  revive  in  supar 
solution.  A  ''salt  action "  is  necessary  to  the  penetration 
of  KCl  in  either  direction  through  the  membrane;  all 
salts,  however,  are  not  equally  effective;  in  the  case  of 
Na  salts  the  effect  shows  an  increase  with  increase  in 
the  valence  of  the  anion.  These  effects  apparently 
indicate  that  the  penetration  of  ions  through  a  membrane 
consisting  of  colloidal  material  with  which  the  ions 
form  compounds  (proteinates)  requires  the  presence  of 
other  free  ions  with  which  the  penetrating  ion  can  form 
alternative  combinations.  Otherwise  it  is  held  in 
position  by  chemical  forces  and  unable  to  move  freely. 
Similar  conditions  have  been  observed  in  the  diffusion 
of  dyes  (neutral  red)  from  stained  eggs;  this  diffusion  is 
also  facihtated  by  the  presence  of  salts  in  the  outer 
medium.  In  order  to  obtain  the  maximum  diffusion- 
facilitating  salt-effect  a  certain  medium  concentration 
of  the  effective  salt  is  required;  higher  concentrations 
and  lower  concentrations  have  a  retarding  influence  on 
diffusion;  this  latter  effect  appears  to  form  the  basis 
of  the  usual  salt-antagonisms  or  protective  effects  shown 
by  calcium  and  other  bivalent  salts.  ^ 

It  is  evident  that  changes  in  the  physical  properties 
of  membranes  must  alter  the  readiness  with  which  diffus- 
ing materials  penetrate,  and  that  such  changes  may  result 
from  changes  in  the  chemical  composition  of  the 
membrane-forming  compounds  as  well  as  from  changes  in 
their  distribution  or  state  of  subdivision.  In  a  membrane 
consisting  of  protein,  the  formation  of  proteinates  with 
varying  physical  properties  will  change  the  permeability 
and  the  other  properties  of  the  membrane.     Similarly 

^Loeb,  Journal  of  Biological  Chemistry  (1916),  loc.  cit. 


176    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

if  lipoids  or  other  ester-like  compounds  are  membrane- 
components,  the  formation  of  soaps  becomes  a  possi- 
bility; these  vary  in  their  solubilities  and  water- 
combining  properties;  and  variations  in  their  proportions, 
e.g.,  the  substitution  of  Ca  soaps  for  Na  or  K  soaps,  will 
entail  corresponding  changes  of  permeability. 

The  question  of  whether  the  protein  or  the  Kpoid 
components  of  the  Hving  plasma  membranes  are  chiefly 
concerned  in  the  variations  of  permeability  underlying 
toxic  effects  or  normal  physiological  processes  is  an  open 
one ;  but  in  all  probability  both  compounds  play  a  part, 
although  the  present  evidence  seems  to  favor  the  view 
that  the  proteins  are  physically  the  more  stable  of  the 
two  and  form  the  permanent  structural  substratum, 
while  variations  of  permeabiHty  depend  chiefly  on 
changes  in  the  Hpoid  components,  especially  the  soaps. 
Parallels  to  the  physiological  salt  antagonisms  are  well 
known  in  non-Hving  systems  containing  both  classes  of 
compounds.  Of  chief  biological  interest  is  the  antago- 
nism between  Na  salts  and  Ca  salts,  which  is  apparently 
universal  in  living  organisms.  Protein  systems  contain- 
ing salts  of  these  two  metals  show  variations  in  properties 
when  the  proportions  of  the  salts  are  varied;  such 
properties  as  water-combining  power  (swelling  or  hydra- 
tion), viscosity,  osmotic  pressure,  susceptibility  to 
alteration  by  organic  compounds  (precipitation  by 
alcohol),  and  electrical  polarization  of  particles  are 
affected;  Loeb's  recent  investigations  afford  instances 
of  salt-antagonisms  affecting  all  of  these  properties.^ 
The  inference  from  such  facts  would  be  that  Ca  and  Na 

^Loeb,  Journal  of  Biological  Chemistry,  XXXI  (191 7),  3;  XXXIV 
(1918),  395,  489;  XXXV  (1918),  497. 


INORGANIC  SALTS  177 

proteinates  must  co-exist  in  certain  definite  proportions 
in  the  cell-structures,  including  the  membranes,  if 
certain  biologically  necessary  physical  properties  are  to 
be  preserved.  Substitution  of  Na  for  Ca  compounds 
would  occur  in  pure  Na  salt  solutions,  with  resulting 
structural  changes  which  might  well  be  injurious  or  fatal. 
Clowes^  has  recently  shown  that  salt-antagonisms 
having  an  even  closer  resemblance  to  biological  salt 
antagonisms  may  be  demonstrated  in  oil- water  emulsion 
systems  by  varying  the  proportions  of  Na  and  Ca  soaps 
in  the  interfacial  films.  The  number  of  separate  drops 
formed  when  a  slightly  alkaline  salt  solution  is  allowed 
to  flow  through  a  stalagmometer  into  oUve  oil  is  found 
to  vary  in  a  remarkable  manner  with  variations  in  the 
proportions  of  NaCl  and  CaCL  in  the  solution;  thus 
with  an  alkaHnity  of  .ooin  NaOH,  the  following  number 
of  drops  per  minute  were  observed  with  different 
solutions : 

c-  ,  ,.  Drops  per 

Solution  ^yiinute 

Control  (no  salt) 44 

Pure  0.15  m  NaCl 300 

Pure  0.0015  m  CaCL 24 

0.15  m  NaCl-ho.0015  m  CaCL 44 

0.3  m  NaCl-ho.003  m  CaCL  : 43 

0.4s  m  NaCl-ho.005  m  CaCL 43 

0.6  m  NaCl-f-o.oi  m  CaClj 43 

The  pure  NaCl  solution  greatly  promotes  the 
tendency  toward  fine  subdivision  of  the  drops;  the 
CaCL  decreases  this  tendency;  at  a  certain  ratio  of  the 
two  salts  (Na:  Ca  about  50  or  100:1)  the  two  tendencies 
counteract    each    other.     The    result    depends   on    the 

^  Clowes,  Journal  of  Physical  Chemistry,  XX  (1916),  407. 


178    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

different  solubilities  of  the  Na-oleate  and  the  Ca-oleate 
in  the  two  phases,  the  former  being  soluble  in  water 
but  not  in  oil,  the  latter  soluble  in  oil  but  not  in  water. 
The  surface-tension  conditions  at  the  interface  are 
accordingly  oppositely  affected  by  the  two  salts,  with 
correspondingly  opposite  effects  on  the  state  of  disper- 
sion; at  a  certain  ratio  of  concentrations  the  two  op- 
posite effects  are  balanced.  Clowes  shows  that  when 
equal  volumes  of  oil  and  alkaline  salt  solution  (mixtures  of 
n/io  Na  OH  and  n/io  CaCy  are  shaken  together,  the 
effect  varies  according  to  the  proportions  of  Na  and  Ca 
in  the  solution;  when  Na  is  present  in  excess,  the  oil  is 
dispersed  as  droplets  in  a  continuous  water  phase,  while 
when  Ca  is  in  excess  the  water  is  dispersed  as  droplets 
in  a  continuous  oil  phase.  A  reversal  of  phase-relations 
may  thus  be  accomplished  in  an  emulsion  system  by 
changing  the  salt-content;  and  this  conclusion  has 
highly  important  biological  applications,  since  it  bears 
closely  on  the  problem  of  the  relations  between  the  lipoid 
and  the  aqueous  components  in  the  living  protoplasmic 
system.  Any  system  in  which  the  oil  (organic  solvent 
or  lipoid)  phase  is  the  continuous  one  is  permeable  to 
oil-soluble  substances,  but  not  to  water-soluble  sub- 
stances which  are  oil-insoluble;  and  the  general  corre- 
spondence of  this  condition  with  that  observed  in  living 
protoplasm  suggests  the  possibility  that  the  external 
layer  of  the  living  plasma  membrane  consists  (at  least 
during  the  greater  part  of  its  existence)  of  a  continuous 
layer  of  lipoid  material,  the  continuous  condition  de- 
pending on  the  presence  of  compounds  with  properties 
like  those  of  Ca  soaps.  The  importance  of  Ca  to 
the    semi-permeability   and    water-resisting    properties 


INORGANIC  SALTS  179 

of  the  protoplasmic  surface-film,  on  this  hypothesis,  is 
evident. 

The  possibility  of  a  reversibility  of  phase-relations 
under  salt  action^  implies  the  possibility  of  inducing 
reversible  changes  of  permeabihty  under  these  conditions, 
and  such  reversible  changes  are,  as  we  have  seen,  a 
characteristic  feature  of  the  living  plasma  meml^ranes. 
Clowes  has  in  fact  constructed  a  model  in  which  an 
emulsion  consisting  of  equal  volumes  of  oil  and  a  mixed 
salt  solution  (containing  NaCl,  KCl,  and  CaCla  in  propor- 
tions similar  to  those  of  sea  water  and  slightly  alkaline) 
is  supported  in  the  interstices  of  a  paper  partition  (sheets 
of  filter  paper)  fixed  in  position  by  rings  of  rubber  in  the 
interior  of  a  U-tube.^  The  electrical  conductivity  of 
the  emulsion-permeated  paper  is  then  found  to  vary, 
when  the  solution  in  contact  with  it  is  changed,  in  a 
manner  resembling  in  general  that  shown  by  the  parti- 
tion of  living  plant-tissue  in  Osterhout's  experiments. 
In  pure  NaCl  solution  the  conductivity  is  rapidly 
increased;  in  pure  CaCla  it  is  decreased;  and  the  changes 
of  conductivity  are  reversible  if  they  are  not  allowed  to 
proceed  too  far.  It  is  assumed  that  in  the  capillary 
interstices  the  emulsion  undergoes  reversible  changes  of 
phase  of  the  above-described  kind,  the  conversion  of  the 

^  For  the  conditions  of  the  reversibility  of  phase-relations  in  emul- 
sions cf.  Ne^\^nan,  Journal  of  Physical  Chemistry,  XVIII  (iqm),  34; 
Briggs  and  Schmidt,  ibid.,  XIX  (1915),  478;  Clowes,  ibid.,  XX  (1916), 
407;  Bhatnagar,  Jour.  Chem.  Soc.  Trans.,  CXVII  (1920),  542;  also 
Physics  and  Chemistry  of  Colloids,  Discussion  of  Faraday  Society  and 
Physical  Society  of  London  (1921),  p.  27;  also  in  Kolloid-Z.,  XX\'1II 
(1921),  206. 

^Clowes,  Proceedings  of  the  Society  of  Experimental  Biology  and 
Medicine,  XV  (1918),  108. 


i8o   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

oil  from  the  continuous  to  the  discontinuous  phase 
corresponding  to  an  increase  in  conductivity  and  vice 
versa. 

It  will  be  remembered  that  water-insoluble  colloidal 
material  (Cua  FeCye)  held  in  the  interstices  of  a  support- 
ing structure  forms  the  essential  composition  of  the  semi- 
permeable membranes  used  in  the  osmotic  pressure 
determinations  of  Pfeffer  and  Morse;  in  such  membranes, 
also,  permeability  is  changed  by  the  action  of  salts. 
The  conditions  in  living  membranes,  while  probably 
similar,  in  the  above  broad  sense,  to  those  in  such 
structurally  composite  membranes,  are  vastly  more 
complex,  chiefly  on  account  of  the  constant  presence  of 
the  metabolic  factor.  Clowes  propounds  the  general 
hypothesis  that  ''variations  in  the  permeability  of  the 
protoplasmic  membranes  are  attributable  to  the  action 
of  electrolytes  and  metabolic  products  on  delicately 
balanced  interfacial  soap-films  and  emulsion  systems, 
and  that  proteins  may  play  no  part  in  the  valve-Hke 
mechanism  controlling  permeability  other  than  to  afford 
a  supporting  filamentous  or  mesh-like  structure."' 

Such  an  arrangement  need  not  be  taken  too  Hterally 
as  an  exact  model  of  the  conditions  in  the  protoplasmic 
surface-films.  It  seems  probable,  however,  that  in  the 
plasma  membrane  there  is  a  combination  of  a  relatively 
permanent  supporting  structure,  presumably  protein, 
with  a  variable  emulsion-like  component  whose  water- 
insoluble  phase  is  normally  so  disposed  as  to  block, 
with  a  considerable  degree  of  completeness,  the  interstitial 
spaces  or  capillary  channels  of  the  membrane.  Varia- 
bility in  this  emulsion,  under  the  influence  of  salt  solu- 

'  Clowes,  op.  cii.y  p.  no. 


INORGANIC  SALTS  i8i 

tions  or  other  factors,  involves  variability  in  the  pcrme- 
abihty  of  the  partition;  and  as  a  secondary  consequence 
other  conditions  depending  on  that  permeabiHty,  such 
as  electrical  polarization,  are  afifected.  Such  a  concep- 
tion implies  that  changes  in  the  supporting  protein 
structure  may  also  influence  permeability;  but  it 
regards  the  normal  or  physiological  variations  in  this 
property  as  dependent  chiefly  on  variations  in  the  state 
of  the  most  external  water-insoluble  or  lipoid  portion  of 
the  protoplasmic  complex.  Such  a  conception  allows 
for  a  wide  range  of  variability  in  the  permeability  of  the 
membrane.  The  latter  is  not  to  be  regarded  as  a  con- 
tinuous lipoid  sheet  under  one  set  of  conditions,  which 
changes  without  transition,  under  other  conditions,  into 
a  state  in  which  the  lipoid  becomes  the  discontinuous 
and  the  aqueous  phase  the  continuous  phase.  A  bal- 
anced state,  with  fluctuations  on  either  side  of  a  mean, 
which  is  regulatively  maintained  by  metabolic  processes, 
is  rather  the  one  to  be  conceived  as  representing  the 
condition  actually  existing  during  life. 

A  simple  case  of  salt-antagonism,  which  I  have 
recently  studied  in  the  starfish  egg,'  appears  to  throw 
hght  upon  the  more  specifically  chemical  conditions  of 
these  phenomena.  The  fully  mature  starfish  egg  (ca. 
i6o  ju  in  diameter)  is  surrounded  with  a  layer  of  jelly-like 
substance,  of  15  to  20  ju  in  diameter,  consisting  of 
water-swollen  material  (of  undetermined  nature)  sepa- 
rated or  secreted  from  the  egg-protoplasm.  11iis  layer 
is  rendered  visible  by  mounting  the  eggs  on  a  slide,  with 
cover-glass,  in  a  suspension  of  India  ink,  to  which  the 
jelly  is  impermeable;   it  then  appears  under  the  niicro- 

'Jour.  Gen.  Physiol.,  Ill  (1921),  783- 


i82    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

scope  as  a  clear  halo  surrounding  each  egg.  When  the 
egg  is  washed  in  pure  isotonic  NaCl  solution  (0.54  m), 
preferably  with  the  aid  of  centrifuging,  the  jelly  swells 
and  dissolves;   but  in  NaCl  solution  containing  a  little 

CaCL   ( —  is   sufficient)   it   remains   intact.     Salts  of 
400 

several  other  metals  (Mg,  Mn,  Co,  Ni,  Al)  have  been 
found  to  have  a  similar  effect.^  The  jelly  layer,  in  the 
presence  of  the  salts  of  sea  water  and  in  mixtures  of 
NaCl  and  CaClz,  thus  possesses  a  certain  water- 
insolubility  and  physical  consistency;  these  properties 
are  apparently  dependent  on  the  presence  of  a  calcium 
compound  (possibly  proteinate)  with  definite  physical 
properties  (especially  water-insolubility  and  lack  of 
tendency  to  swell)  which  preserves  the  characteristic 
structure  and  consistency  of  the  whole  layer.  In  pure 
NaCl  solution  this  constituent  is  replaced  by  the  corre- 
sponding sodium  compound  which  is  water-soluble  and 
swells  readily,  hence  the  coherence  and  insolubility  of 
the  layer  as  a  whole  are  lost. 

This  process  may  be  regarded  as  a  model  of  the 
essential  kind  of  change  occurring  in  the  plasma  mem- 
branes of  living  cells  in  pure  NaCl  solution.  The 
surface  of  the  starfish  egg  is  in  fact  physically  altered 
by  NaCl  solution  in  a  characteristic  manner;  unfertilized 
eggs  placed  in  the  pure  solution  cohere  in  clumps  or 
agglutinate;  many  eggs  also  form  fertilization-membranes 
(when  returned  to  sea  water)  and  show  evidence  of 
partial  activation  by  cleaving  and  in  some  cases  develop- 
ing to  the  blastula  stage.     All  of  these  effects  of  the  pure 

^  Unpublished  experiments  in  the  Nela  Research  Laboratory  at  the 
Marine  Biological  Laboratory  at  Woods  Hole. 


INORGANIC  SALTS  183 

solution  are  prevented  in  the  presence  of  a  lilllc  CaCl,. 
The  toxic  action  of  the  pure  solution  and  also  its 
membrane-forming  action  are  correlated  with  a 
permeability-increasing  action,  as  in  the  other  cases 
cited  above;  and  the  correspondence  with  the  bcha\iur 
of  the  jelly  seems  to  imply  that  the  increase  of  permea- 
bility in  the  pure  solution  is  to  be  referred  also  to  the 
replacement  of  water-insoluble  Ca  compounds  (e.g., 
Ca  proteinates  or  soaps),  on  which  the  properties  of 
the  plasma  membrane  depend,  by  soluble  Na  compounds. 
There  is  much  independent  evidence  that  this  role 
of  calcium  compounds — i.e.,  of  determining  the  properties 
of  the  surface  layers  of  cells — is  a  general  one;  we  may 
thus  understand  the  importance  of  Ca  to  all  normal 
cell-processes  (stimulation,  etc.)  w^hich  depend  on  changes 
in  the  surface  layers.  The  peculiar  relation  of  Ca  to 
the  coherence  of  blastomeres  and  of  plant  cells  has 
already  been  mentioned;  according  to  the  earlier  work 
of  Mangin,  Ca  compounds  (''Ca-pectate")  in  the  middle 
lamella  of  plant  cells  are  essential  to  the  structural 
coherence  of  cellular  tissues;  when  the  Ca  is  replaced 
by  Na,  the  cells  tend  to  fall  apart.  Similar  phenomena 
are  also  well  known  in  the  epithelial  tissues  of  animals; 
e.g.,  in  the  ciliated  epithelium  of  Mitylus  the  cells  swell 
and  fall  apart  in  pure  solutions  of  many  Na  and  K  salts, 
and  this  effect  is  prevented  by  Ca.'  Recently  the 
changes  occurring  in  plant  tissues  in  pure  NaCl  solutions 
have  been  studied  in  much  detail  by  Hansteen.^     The 

^  R.  S.  Lillie,  American  Journal  of  Physiology,  XVII  (1906),  89;  cf. 
p.  122. 

^Hansteen  (Hansteen-Cranner),  Jahrh.  wiss.  Botanik,  XIA'II 
(1910),  374;  LIII  (1913-14),  536;  Bcr.  dcutsch.  Bolan.  Gcs.,  XXXVII 
(1919),  380.  Also  his  recent  book,  Zur  Biochemic  u.  Physiologic  dcr 
Grenzschichten  lebender  Pflanzenzellen,  Kristiania  (1922). 


i84    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

general  effects  are  swelling,  loss  of  consistency  or  turgor, 
and  disintegration  of  the  tissue,  accompanied  by  loosen- 
ing of  intercellular  coherence;  these  effects  are  all 
prevented  or  greatly  decreased  in  the  presence  of  a 
little  Ca.  Hansteen  believes  that  water-insoluble  Ca 
compounds  are  essential  constituents  of  living  protoplasm 
in  general,  and  that  they  are  present  especially  in  the 
protoplasmic  surface  layers  and  other  solid  structures; 
he  also  cites  evidence  indicating  that  these  compounds 
are  lipoid  in  nature.  According  to  his  conception, 
pure  alkali  salt  solutions  attack  the  surface  layers  of 
cells  because  they  alter  the  water-insoluble  Ca-lipoid 
compounds  there  present,  converting  them  into  water- 
soluble  compounds  and  secondarily  inducing  absorption 
of  water  and  structural  breakdown.  Such  effects  are 
apparently  of  the  same  nature  as  the  disintegration  of 
the  cilia  of  marine  animals  (Arenicola)  and  the  general 
loss  of  semi-permeability  of  plant  and  animal  cells  in 
pure  salt  solutions,  already  described.  They  are  con- 
sistent with  the  general  view  that  in  the  formation  of  the 
solid  or  permanent  (water-insoluble)  protoplasmic  struc- 
tures, Ca  compounds  play  an  essential  part.  Hansteen 
found  that  the  presence  of  more  than  the  normal  concen- 
tration of  Ca  salts  in  culture  solutions  favored  profuse 
branching  and  the  formation  of  an  abundance  of  root 
hairs  in  seedlings;  Wiechmann,  in  Hober's  laboratory, 
has  recently  confirmed  this  result,  and  has  found  further 
that  Sr,  Ba,  and  a  few  heavy  metals  (Mn,  Ni,  Co)  act 
similarly  to  Ca,  while  Mg  is  ineffective.^  It  would 
seem  that  certain  necessary  physical  properties  of 
protoplasmic  structures,  such  as  rigidity,  water- 
^  Wiechmann,  Arch.  ges.  Physiol.,  CLXXXII  (1920),  99. 


INORGANIC  S.\LTS  185 

insolubility,  and  impermeability  to  water-soluble  sub- 
stances (like  sugar  and  salts),  require  the  presence  of 
Ca  compounds.  These  compounds  impart  the  necessary 
structural  stability  to  the  whole  protoplasmic  complex. 
A  fact  of  interest  in  relation  to  this  question  is  Meigs's 
recent  observation  that  an  approach  to  semi-permeability 
can  be  imparted  to  certain  artificial  colloidal  membranes, 
otherwise  highly  permeable,  by  depositing  insoluble  Ca 
salts  (phosphate)  in  their  substance.^ 

These  facts  and  considerations  are  consistent  with 
the  view  that  Ca  compounds,  e.g.,  Ca  soaps,  play  a 
similar  part  in  the  surface  layers  of  protoplasm,  and  the 
recent  interesting  experiments  of  Clark^  with  the  frog's 
heart  lend  support  to  this  general  conception.  He  finds 
that  the  heart,  after  being  weakened  by  prolonged 
perfusion  with  Ringer's  solution,  rapidly  regains  its 
vigor  if  perfused  with  Ringer's  solution  to  which  serum, 
serum-lipoids,  lecithin,  or  soaps  of  higher  fatty  acids, 
have  been  added.  During  perfusion  with  pure  Ringer's 
solution  the  heart  loses  to  the  solution  some  material 
which  has  a  similar  reviving  action  when  perfused 
through  other  exhausted  hearts.  In  order  that  these 
substances,  or  soap,  should  exhibit  this  beneficial  action, 
calcium  must  be  present.  He  concludes  that  the  benefi- 
cial action  of  the  soaps  is  associated  with  the  adsor]:)tion 
of  a  water-soluble  Ca  soap  or  similar  compound  upon  the 
surface  of  the  muscle  cells,  and  puts  forward  the  hypothe- 
sis ''that  the  activity  of  the  heart  is  dependent  upon  the 
semi-permeability  of  the  cell  to  electrolytes,  that  this  is 

^  Meigs,  American  Journal  oj  Physiology,  XXXVIII  (191 5).  456. 
="  A.  J.  Clark,  Journal  of  Physiology,  XLVII  (1913),  66;  also  Clark 
and  Daly,  ihid.,  LIV  (1921),  367. 


i86    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

dependent  on  the  presence  of  Ca  and  lipoids  at  the 
surface  of  the  cells,  and  that  during  perfusion  the  heart 
loses  lipoids  and  becomes  more  permeable  to  electro- 
lytes." This  conception  of  semi-permeability  as  depend- 
ent on  the  presence  of  lipoids,  and  of  the  state  of  the 
lipoids  as  determined  by  the  salts  of  the  medium,  is  in 
harmony  with  much  recent  work.'  It  also  affords  a 
point  of  view  from  which  it  is  possible  to  understand 
why  the  physiological  effects  of  salts  and  of  lipoid- 
solvent  compounds  should  have  so  much  in  common. 

^Blackman,  "The  Plasmatic  Membrane  and  Its  Organization," 
New  Phytologist,  XI  (191 2),  180;  Clowes,  loc.  cit;  Czapek,  Oberfldchen- 
spannung  der  Plasmahaui,  Jena  (191 1);  McDougall,  Science,  LV  (1922), 
653;  Hansteen-Cranner,  loc  cit.  See  also  StUes's  review  of  the  subject 
of  cell  permeability  in  New  Phytologist,  XX,  XXI,  XXII  (1921-23). 


CHAPTER  IX 

GENERAL  PHYSIOLOGICAL  ACTION  OF  LIPOID- 
ALTERANT  AND  SURFACE-ACTIVE 
SUBSTANCES 

From  the  physiological  point  of  view  the  reversible 
forms  of  salt  action  are  the  important  ones;  the  proper- 
ties and  activities  of  living  protoplasm  may  thus  be 
modified  by  changing  the  salt-content  of  the  medium, 
and  return  to  the  normal  when  the  original  salt-content 
is  restored.  Such  reversible  effects  are  of  special 
biological  interest,  since  their  essential  conditions  are  in 
all  likelihood  similar  to  those  controlling  the  normal 
variations  of  activity.  Substances  are  continually  being 
formed  in  metabolism  (e.g.,  CO2  and  other  acids)  which 
directly  influence  protoplasmic  action.  It  is,  therefore, 
of  fundamental  interest  to  note  the  existence  of  another 
large  class  of  substances,  many  of  which  are  chemically 
indifferent,  i.e.,  not  readily  oxidized  or  reduced  (hydro- 
carbons and  their  substitution-products),  which  have  a 
profound  influence  on  protoplasm,  completely  reversible 
within  wide  limits.  These  substances  are  those  organic 
compounds,  varying  widely  in  their  chemical  nature, 
which  have  in  common  two  general  physical  properties: 
(i)  a  solvent  action  on,  or  solubility  in,  the  water-insoluble 
organic  constituents  of  protoplasm  (fats,  lipoids,  etc.); 
and  (2)  a  high  degree  of  surface-activity,  i.e.,  influence 
on  the  surface-tension  at  the  boundary  between  water 
and  non-aqueous  phases.  These  compounds  appear  also 
to  produce   their  physiological  effects  by  altering   the 

187 


1 88    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

structural  substratum  of  protoplasm  in  a  manner  which 
does  not  permanently  change  its  properties  or  physical 
state.  Hence  in  their  presence  physiological  processes 
are  modified  temporarily  in  rate  or  character,  and  resume 
their  former  conditions  when  the  substance  is  removed. 
The  special  affinity  of  these  compounds  for  substances 
having  fat-like  properties  indicates  that  their  primary 
action  is  on  the  lipoid  constituents  of  protoplasm;  their 
possible  action  on  proteins,  however,  is  also  to  be  consid- 
ered. In  general  they  include  the  substances  comprised 
in  Overton's  first  group  (alcohols,  ethers,  esters,  normal 
and  substituted  hydrocarbons,  etc.). 

We  distinguish,  therefore,  two  chief  groups  of  com- 
pounds which  by  means  of  their  reversible  influence  on 
the  structural  substratum  of  protoplasm  may  modify 
vital  processes  without  affecting  them  permanently  or 
injuriously:  (a)  neutral  salts  or  other  electrolytes 
(acid  and  alkali),  and  (b)  lipoid-solvent  or  surface-active 
organic  compounds.  These  two  groups  may  be  charac- 
terized respectively  as  general  colloid-alterants  and 
lipoid-alterants.  The  compounds  of  these  groups  differ 
somewhat  sharply  in  their  physiological  action  from  those 
compounds  whose  chemical  effects  tend  to  be  irreversible; 
the  latter  include  most  of  the  strong  oxidizing  and  reduc- 
ing agents  and  the  salts  of  heavy  metals;  usually  these 
are  not  capable  of  modifying  physiological  processes  with- 
out permanent  injury;  hence  they  are  toxic  or  poisonous 
in  small  doses.  Recovery  from  the  effects  of  this ' '  poison- 
ous" group  depends  upon  the  reparative  activity  of 
the  living  protoplasm,  just  as  does  recovery  from  mechan- 
ical injury,  and  not  upon  a  simple  reversal  of  the  chemical 
or  other  action  of  the  compound. 


LIPOID-ALTERANT  SUBST/VNCES  189 

The  most  remarkable  general  physiological  ciTcct 
produced  by  the  lipoid-alterant  substances  is  a  reversible 
suppression  of  irritability  or  spontaneous  activity. 
This  effect  always  appears  in  certain  definite,  not  too 
high,  concentrations  of  these  compounds,  and  constitutes 
the  phenomenon  of  narcosis  or  anaesthesia,  which  is 
universal  in  living  matter.^  The  power  of  inducing 
this  state  seems  to  be  independent  of  the  special  chemical 
nature  of  the  narcotizing  compound;  evidently  this 
power  is  connected  in  some  manner  with  the  general 
physical  properties  just  named;  and  the  question  first 
arises  whether  the  lipoid-solubility  of  these  compounds 
or  their  surface-activity  is  the  property  primarily 
responsible  for  this  characteristic  action. 

CORRELATION  BETWEEN  PHYSIOLOGICAL  ACTION  AND 

LIPOID-SOLUBILITY 

The  existence  of  a  relation  between  the  solubility  of 
chemical  compounds  in  fats  and  their  narcotic  action 
was  early  noted,  first  by  Bibra  and  Harless  in  1847,  and 
later  by  Claude  Bernard,  Hermann,  Richet,  Ehrlich, 
and  others.''  Richet  propounded  the  rule  that  any 
narcotizing  compound  has  the  stronger  action  as  a 
narcotic  the  lower  its  solubility  in  water.  This  is 
similar  to  the  rule  of  Overton  and  iMeyer  that  the 
narcotic  effectiveness  of  a  compound  runs  parallel  with 

^  "We  may  say  that  everything  living  is  sensitive  and  can  be 
anaesthetized;  whatever  is  not  sensitive  is  not  living  and  cannot  be 
anaesthetized."— Claude  Bernard,  address,  "La  Sensibility"  (delivered 
in  1876),  published  in  his  book,  La  Science  ExpCrimcnlak,  Paris  (1S90). 

2  Cf.  Overton,  Stiidien  iiber  die  Narkose,  Jena  (1901),  for  a  historical 
account  of  the  earlier  work  on  narcosis. 


I  go    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

its  oil-water  partition-coefficient,  a  relation  first  studied 
systematically  by  these  investigators/ 

In  his  investigations  on  permeability,  Overton  had 
reached  the  conclusion  that  solubility  in  lipoids  was  the 
chief  factor  determining  the  entrance  of  compounds 
into  cells;  such  readily  penetrating  compounds  belong 
for  the  most  part  to  the  narcotizing  group;  and  a 
detailed  study  of  the  phenomena  of  narcosis  in  tadpoles 
demonstrated  a  close  parallelism  between  the  relative 
solubilities  of  a  large  number  of  organic  compounds  in 
oil  and  water  and  their  narcotizing  action.^  The  ratio 
according  to  which  any  compound  is  distributed  between 
these  solvents  (when  the  solvents  are  in  contact  and 
equilibrium  is  reached)  is  a  measure  of  its  relative  solu- 
bility in  the  two;  this  ratio  is  known  as  the  ''partition- 
coefficient."  In  the  early  members  of  any  homologous 
series  of  compounds  the  ratio  of  oil-solubility  to  water- 
solubility  increases  progressively  as  the  molecular 
weight  increases,  and  the  same  is  true  of  the  narcotizing 
properties  of  the  compounds.  For  example,  with  the 
ethyl  esters  of  the  first  five  fatty  acids,  Overton  found 
the  concentrations  required  for  the  complete  narcosis 
of  tadpoles  to  be  as  indicated  in  the  table  (p.  191). 

The  narcotic  effectiveness  of  the  ester  increases 
regularly  as  its  water-solubility  decreases;  and  in 
general  each  member  of  the  series  is  from  two  to  three 
times  as  effective  as  its  immediate  predecessor.  Rela- 
tions of  a  similar  kind  were  found  with  other  series, 

^  Overton,  Vierteljahrschriften  d.  Naturf.  Gesellschaft,  Zurich, 
XLIV  (1899),  88;  Studien  iiber  die  Narkose  (1901);  H.  H.  Meyer, 
Arch.f.  exper.  Path.  u.  PharmakoL,  XLII  (1899),  109. 

2  Studien  iiber  die  Narkose. 


LIPOID-ALTERANT  SUBSTANXES  191 

including  hydrocarbons,  alcohols,  aldehydes,  ketones, 
ethers,  and  various  substituted  compounds.  Any 
increase  in  the  oil-water  partition-coefficient  was  associ- 
ated with  increase  in  narcotic  effectiveness.  Overton 
accordingly  drew  the  conclusion  that  the  narcotics  act 
by  dissolving  in  certain  oil-like  or  fatty  constituents  of 
the  irritable  cells  (in  this  case  nerve  cells);  and  he 
identified  these  constituents  with  the  lii)oids,  especially 
lecithin  and  cholesterol,  which  appear  to  be  always 
present  in  protoplasm.  The  essential  determining  con- 
dition of  anaesthesia,  according  to  his  view,  is  the  solution 

■p-fp.  Narcotizing  Concentrations  Solubilities  in  Oil 

^^'^^  (Mols.  per  litre)  and  Water 

Ethyl  formate .07  to  .09  m  Oil:  water  4:  i 

Ethyl  acetate -03  m  In    15.2  parts  water; 

in  all  parts  oil 
Ethyl  propionate. . .  .01  to  .012  m         In    50    parts  water; 

in  all  parts  oil 
Ethyl  butyrate .0043  m  In  190  parts  water; 

in  all  parts  oil 
Ethyl  valerianate .. .  .0019  m  In  500  parts  water; 

in  all  parts  oil 

of  the  narcotic  compound  in  these  cell  constituents; 
when  the  lipoids  are  charged  or  impregnated  with  the 
compound,  they  undergo  a  change  of  physical  properties, 
entailing  corresponding  alterations  in  the  irritability  of 
the  cell.  Meyer  drew  independently  a  similar  conclu- 
sion;' he  pointed  out  that  the  narcotizability  of  cells 
seems  to  be  related  to  the  nature  and  proj^ortion  of  the 
lipoids  present  in  the  protoplasm;  e.g.,  the  high  suscepti- 
bihty  of  nerve  cells  to  narcosis  is  a  correlative  of  their 
high  Kpoid-content.  Different  narcotics  act  unequally 
because  they  are  distributed  in  unequal  ratios  between  the 

'^  Meyer,  loc.  ciL 


192    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

lipoid  and  the  aqueous  phases  of  protoplasm;  in  general, 
the  greater  the  relative  lipoid- solubility,  the  larger  the 
proportion  of  the  anaesthetic  compound  which  is  in 
solution  in  the  Kpoids  when  the  partition-equilibrium  is 
reached.  Hence  when  a  compound  has  a  very  high 
Hpoid-solubihty  it  may  exert  narcotic  action  in  extremely 
dilute  solution;  phenanthrene,  for  example,  was  found 
by  Overton  to  narcotize  tadpoles  in  dilutions  of  one  part 
in  1,500,000  of  water. 

The  general  conception  known  as  the  ''Overton- 
Meyer  theory  of  narcosis"  may  be  defined  as  follows. 
The  solubility  of  narcotizing  compounds  in  the  cell- 
hpoids  forms  the  basis  of  their  narcotic  and  presumably 
other  pharmacological  properties.  By  dissolving  in  the 
lipoids,  such  compounds  alter  the  physical  properties 
of  these  essential  components  of  the  protoplasmic 
system,  and  hence  all  properties  of  the  system,  especially 
irritability,  which  are  dependent  on  the  state  of  the 
Hpoids.  Since  simple  solution  without  chemical  combi- 
nation is  the  basis  of  this  effect,  the  latter  is  readily 
reversed  by  allowing  the  compounds  to  diffuse  away. 

The  general  conclusion  that  selective  solubility  is 
the  essential  basis  of  narcotic  action  does  not,  however, 
necessarily  follow,  since  the  same  reasoning  would 
apply  to  other  physical  effects  which  are  reversible  under 
similar  conditions;  e.g.,  effects  dependent  on  surface- 
activity,  involving  a  lowering  of  surface-tension  at  the 
protoplasmic  phase-boundaries  and  a  concentration  of 
the  narcotizing  compound  at  these  surfaces.  Probably, 
however,  the  case  is  not  one  of  alternatives;  if  lipoids 
are  present  in  the  system,  any  substances  which  are 
soluble  in  these  components  must  inevitably  dissolve 


LIPOID -ALTERANT  SUBSTANCES  193 

according  to  the  partition-ratios.  /Vny  tendency  to 
concentrate  at  surfaces  (e.g.,  the  general  cell  surface  or 
the  surfaces  of  other  lipoid-containing  i)rot()phisniic 
structures)  would  be  favorable  to  such  solution;  i.e., 
would  render  it  more  rapid  and  greater  in  degree  than 
it  would  be  otherwise,  since  the  partition-equilibrium 
would  then  be  between  the  solution  in  contact  with  the 
surface  of  the  Hpoid  particle  and  the  solution  in  the 
interior  of  the  particle. 

Meyer's  experiments  on  the  influence  of  temperature 
on  the  critical  anaesthetizing  concentrations  of  certain 
compounds'  gave  further  indications  that  the  solubility 
of  these  compounds  in  the  cell-lipoids  is  the  essential 
factor  in  the  physiological  effect.  He  chose  six  com- 
pounds whose  oil-water  partition-ratios  vary  considerably 
with  temperature,  and  determined  the  minimal  concen- 
trations required  to  anaesthetize  tadpoles  at  the  two 
temperatures  3°  and  30°.  These  concentrations  arc 
given  in  the  following  table : 

.        .,    .•  Critical  Concentration  Oil-Water  Partition- 

Anesthetic  fQ^  Anesthesia  Coefficients 

At  3°  At  30°  At  3°  At  30° 

(A)  Salicylamide m/1300  m/600  22. 23  14 

Benzamide m/500  m/200  0.67  0.43 

Monoacetin m/90  m/70  0.099  0.066 

(B)  Ethyl  Alcohol m/3  m/7  0.026  0.247 

Chloral  Hydrate. . .   m/50  m/250  0.053  0.236 

Acetone m/3  m/7  o.  146  o.  235 

In  the  first  three  compounds  (A)  the  relative  lipoid- 
solubility  decreases  with  rise  of  temperature,  and  the 

'Meyer,  Arch.  f.  cxper.  Palh.  u.  Pharmakol.,  XLVI  (1901),  338. 
Recently  Mary  E.  Collett  has  investigated  the  effects  of  variation  of 
temperature  on  the  narcotic  action  of  various  compounds  on  marine 
organisms;  of.  Proceedings  of  the  Society  for  Experinientnl  Biology  and 
Medicine,  XX  (1923),  259. 


194    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

critical  narcotizing  concentration  increases;  in  the  last 
three  (B)  the  conditions  are  reversed.  Tadpoles  com- 
pletely anaesthetized  at  30°  in  m/250  chloral  hydrate 
revive  and  become  active  on  cooling  the  solution;  on 
warming  they  again  become  inactive.  Such  an  effect 
is  difficult  to  explain  except  on  the  basis  of  the  greater 
lipoid-solubility  of  the  anaesthetic  at  the  higher  temper- 
ature, since  adsorption  is  in  general  increased  by  lowering 
the  temperature.  Meyer  therefore  concludes  that  the 
anaesthetic  produces  its  effect  by  dissolving  in  the  cell- 
lipoids.  Such  experiments  seem  to  indicate  clearly  that 
the  solvent  action  of  the  protoplasmic  lipoids  is  a  main 
factor  in  anaesthesia;  and  since  anaesthesia  has  close 
affinities  with  normal  variations  of  irritabihty,  such  as 
sleep  and  fatigue,  they  also  point  to  the  conclusion  that 
under  normal  conditions  the  lipoids  are  important  in  the 
cell  largely  because  of  their  peculiar  properties  as  solvents. 

The  relation  of  the  solvent  properties  of  lipoids  to 
permeabihty  has  already  been  considered.  The  lipoids 
thus  represent  the  organic  solvents  of  the  cell,  and 
apparently  the  properties  of  the  protoplasmic  system 
vary  according  to  the  nature  and  concentration  of  the 
substances  which  they  hold  in  solution.  This  is  a 
conclusion  of  much  general  interest,  apart  from  its 
special  relation  to  anaesthesia,  since  variations  in  the 
proportions  of  water-soluble  to  lipoid-soluble  substances 
no  doubt  occur  constantly  in  Hving  protoplasm.  The 
question  of  why  such  variations  alter  irritability,  spon- 
taneous activity,  and  metabohsm  will  be  considered 
more  fully  later  in  connection  with  stimulation. 

In  many  cases  it  has  been  shown  that  the  organic 
anaesthetics  accumulate  in  cells  in  greater  concentration 


LIPOID-ALTER.\NT  SUBSTANCES  195 

than  in  the  medium,  and  this  fact  is  usually  interpreted 
as  favoring  the  partition  theory  of  narcosis.  Pohl' 
found  that  the  blood  corpuscles  and  brain  of  deeply 
narcotized  dogs  contained  from  three  to  four  times  as 
much  chloroform  as  the  serum;  Hedin'  investigated 
cryoscopically  the  distribution  of  alcohols,  aldehydes, 
ketones,  esters,  and  ether  between  corpuscles  and 
plasma,  and  found  that  most  compounds,  especially  the 
more  highly  lipoid-soluble,  collected  in  higher  concentra- 
tion in  the  cells  than  in  the  plasma.  More  recently 
Warburg  and  WieseP  have  made  similar  obser\'ations  on 
the  blood  corpuscles  of  birds,  using  alcohols,  ketones, 
urethanes,  thymol,  formaldehyde,  and  HCX.  All  of 
these  compounds,  in  appropriate  concentrations,  were 
found  to  decrease  oxygen  consumption,  and  the  tendency 
to  concentrate  in  the  cells  ran  closely  parallel  with  this 
effect.  Thus  the  low^r  alcohols  (up  to  butyl  alcohol) 
were  the  least  effective  in  reducing  oxygen  consumption, 
and  showxd  correspondingly  a  somewhat  lower  solubility 
in  the  protoplasm  than  in  the  medium;  methyl  urethane, 
diethyl  urea,  and  acetone  behaved  similarly:  amyl 
alcohol  and  isobutyl  urethane  were  more  effective,  and 
were  about  equally  distributed  between  cells  and  medium ; 
while  the  most  effective  substances — phenyl-mcth}'l 
ketone,  thymol,  phenyl  urethane — all  showed  decided 
concentration  in  the  cells.  When  solutions  were  used 
that  decreased  the  oxygen  consumption  by  50  per  cent, 
phenyl-methyl  ketone  was  found  to  be  about  twice, 
phenyl  urethane  three  times,  and  th}'mol  nine  times  as 

'Pohl,  Arch,  exper.  Path.  u.  Pharmakol.,  XXVIII  (1891),  239. 

'Hedin,  Arch.  ges.  Physiol.,  LX\TII  (1897),  229. 

3  Warburg  and  Wiesel,  Arch.  ges.  Physiol.,  CXLIV  (191 2),  465. 


196    PROTOPLASMIC  ACTION  AND  N'ERVOUS  ACTION 

concentrated  in  the  cells  as  in  the  medium.  Formal- 
dehyde and  HCN  also  underwent  concentration  in  the 
cells.  The  series,  methyl  alcohol  <  butyl  alcohol  <amyl 
alcohol  <  phenyl -methyl  ketone  <  phenyl  ure  thane  < 
thymol  represents  the  order  both  of  increasing  physio- 
logical action  and  of  increasing  concentration  in  the 
cells. 

On  the  whole  the  foregoing  studies  of  the  distribution 
of  narcotics  between  cell  and  medium  appear  to  favor  the 
partition  theory  of  the  action  of  these  compounds.  It 
should  be  pointed  out,  however,  that  the  order  of  relative 
adsorption  is  in  general  the  same  as  that  of  hpoid- 
solubility .  The  probabiUty,  as  already  pointed  out,  is  that 
both  solution  and  adsorption  are  factors  in  the  total  effect. 

CORRELATION  BETWEEN  PHYSIOLOGICAL  ACTION 
AND  SURFACE -ACTIVITY 

The  relation  between  the  narcotic  or  other  physio- 
logical action  of  organic  compounds  and  their  influence 
on  surface-conditions  has  recently  received  much  investi- 
gation. The  majority  of  compounds  of  the  lipoid- 
alterant  group  have  a  marked  influence  in  lowering  the 
surface-tension  at  the  boundary-surfaces  between  their 
aqueous  solutions  and  air  or  other  adjoining  phase; 
at  the  same  time,  in  accordance  with  the  Gibbs-Thomson 
rule,  they  undergo  increase  of  concentration  (or  adsorp- 
tion) at  such  surfaces.  In  homologous  series  both  the 
influence  on  surface-tension  and  the  degree  of  adsorption 
increase  progressively  with  increase  in  molecular  weight; 
and  the  view  that  the  physiological  action  is  determined 
by  this  surface-action,  i.e.,  by  the  condensation  of  the 
compounds  at  the  protoplasmic  phase-boundaries,  rather 


LIPOID-ALTERANT  SUBSTANCES  197 

than  by  solution  in  the  Hpoids  has  been  supported  by 
many  recent  investigators,  especially  Czapek,  Traubc, 
and  Warburg.^ 

The  general  fact  that  the  physiological  acticm  of 
homologous  compounds  increases  progressively  with 
increase  in  molecular  weight  has  long  been  noted. 
Richardson,''  in  1869,  in  a  study  of  the  pharmacological 
action  of  alcohols,  called  attention  to  this  rule,  which 
applies  also  to  the  effects  on  lower  organisms;  thus, 
according  to  Regnard,^  the  first  six  alcohols  have  equal 
effects  in  suppressing  the  growth  of  yeast  in  the 
following  concentrations: 

Alcohol  Volumes 

(per  cent) 

CH3OH 20 

GHsOH 15 

C3H7OH 10 

C4H9OH 2.5 

CsH.xOH I 

C6H13OH 0.2 

In  a  series  of  papers  beginning  in  1904,  Traube  has 
directed  special  attention  to  the  parallelism  between 
surface-activity  and  physiological  action.''    For  example, 

^  Czapek,  Oberflachenspanmmg der  Plasmahaul,  Jena  (igi i) ;  Traul>c, 
"Theorie  der  Narkose,"  Arch.  ges.  Physiol.,  CLIII  (1913),  276;  CLX 
(1915),  501.  Cf.  also  "Theorie  des  Haftdrucks  und  Lipoidtheorie," 
Biochem.  Z.,  LIV  (1913),  305,  and  other  papers  there  cited.  Warburg, 
see  below. 

*  Richardson,  "Physiological  Researches  on  Alcohols,"  Medical 
Times  and  Gazette,  VIII  (1869)  (cited  from  Czapek,  loc.  cii.). 

3Regnard,  Compt.  rend.  Soc.  Biol,  X  (1889),  124-  Warburg  and 
Wiesel  obtained  similar  results  with  the  series  of  urcthancs  {loc.  (it.). 

4 Traube,  Arch.  ges.  Physiol,  CV  (1904),  541,  559,  further  refer- 
ences in  the  papers  cited  above. 


198    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

the  surface- tensions  (against  air)  of  0.25  m  aqueous  solu- 
tions of  alcohols  decrease  in  regular  order  as  follows: 

Aio^T^^i  Surface-Tension 

^'''"^^^  (Mgms.  per  mm.) 

CH3OH 7.05 

CaHsOH 6.73 

CjHvOH 2.89 

C4H9OH 4-49 

CsH,,OH 3.05 

(H.0) (7.3) 

The  order  of  relative  adsorption  by  charcoal  and  other 
adsorbents  is  similar;  if  the  degree  of  adsorption  runs 
parallel  with  the  lowering  effect  on  surface-tension,  and  if 
equal  adsorption  corresponds  to  equal  physiological 
action,  we  should  expect  that  solutions  of  the  same 
surface-tension  (isocapillary  solutions)  would  have  the 
same  physiological  effect.  Czapek  and  Traube  have  in 
fact  demonstrated  a  close  parallehsm  between  the  influ- 
ence of  a  large  number  of  compounds  on  air- water  surface- 
tension  and  their  physiological  action.  Traube  has 
called  attention  to  the  fact  that  in  a  homologous  series 
of  compounds  the  degree  of  activity,  both  physical  and 
physiological,  increases  very  generally  about  three  times 
with  each  increase  in  molecular  weight.  According  to 
this  rule  the  isocapillary  concentrations  of  the  successive 
compounds  of  the  series  should  diminish  in  geometrical 
progression,  with  one-third  as  exponent,  as  the  molecular 
weight  increases.  He  gives  the  following  determinations 
for  the  series  of  alkyl  acetates: 

Ester  and  Concentration  Capillary  Height 

CH3COOCH3..  (m)  58.1m 

C,Hs (m/3)  58.0 

C3H7 (m/9)  57.7 

i-C4H9 (m/27)  58.8 

i-CsHxx (m/8i)  59.9 

(H,0) (91. S) 


LIPOID-ALTERANT  SUBSTANCES  199 

In  a  considerable  number  of  cases  the  degree  of  ])hysio- 
logical  action  has  been  shown  to  follow  a  similar  rule; 
the  observations  of  Fiihner  on  haemolysis  (cited  below) 
are  a  good  example. 

If  physiological  activity  is  in  fact  a  function  of  capil- 
lary activity,  solutions  of  equal  surface-tension  should 
exhibit  equal  narcotic  action  or  otherwise  produce  equal 
effects  in  protoplasm;  and  Czapek  has  brought  forward 
evidence  that  this  is  very  frequently  the  case.'  Using 
a  large  number  of  surface-active  organic  compounds,  he 
determined  the  surface-tensions  of  those  solutions  which 
had  equal  effect  in  liberating  tannin  from  plant  cells 
(chiefly  the  leaves  of  Echeveria) ;  this  effect  depends  on 
a  permeability-increasing  action  analogous  to  that 
accompanying  cytolysis.  In  general  he  finds  that  solu- 
tions of  a  concentration  just  sufficient  to  cause  exosmosis 
of  tannin  have  very  nearly  the  same  surface-tension 
against  air;  viz.,  about  two-thirds  that  of  pure  water; 
according  to  his  hypothesis,  the  surface-tension  of  the 
protoplasm  becomes  zero  in  such  solutions  and  an 
effective  surface  of  separation  ceases  to  exist.  Kisch'' 
also  finds  that  isocapillary  solutions  of  alcohols  have  equal 
effects  in  liberating  invertase  from  yeast  and  molds 
and  in  inhibiting  the  growth  of  yeast  cells;  and  II. 
Zuckerkandl-^  has  observed  a  similar  relation  in  the 
protoplasmic  streaming  of  plant  cells.  According  to 
Traube  and  others,  haemolysis  follows  the  same  ruk-.-' 

^  Czapek,  loc.  cil. 

*  Kisch,  Biochem.  Zeitschrijt,  XL  (1912),  152. 

3H.  Nothmann-Zuckerkandl,  Biochem.  Zeitschrijt,  XLV  (1912),  412. 

"Traube,  loc.  cil.;  Fuhner  and  Neubaucr,  Zcnlralbl.  f.  PhysioL^ 
XX  (1906),  117;  Arch,  cxper.  Path.  u.  Plhirmakol.,  LVI  (1907),  333- 


200    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

The  following  table  summarizes  some  of  the  results  of 
Czapek  and  Kisch  with  alcohols. 

Critical  surface-tensions  (water  =  i)  of  solutions  causing 
Alcohol  A.    Exosmosis  of  Tannin  from  B.     Inhibition  of 

Cells  of  Echeveria  Growth  of  Yeast 

Methyl 0.7  0,51 

Ethyl 0.67  0.48 

N-propyl. .  . .  0.675  ca.  0.49 

I-propyl 0.69  

N-butyl 0.69  

I-butyl 0.665  ca.o.s 

I-amyl o .  665  o .  49 

Czapek's  ascription  of  the  effects  which  he  observ^es 
to  a  definite  or  critical  lowering  of  the  surface-tension 
of  the  plasma  membrane  is,  however,  of  doubtful  validity, 
since  there  is  no  necessary  parallelism  between  the 
influence  of  a  given  substance  on  the  surface-tension 
at  a  water-air  interface  and  its  influence  on  the  tensions 
at  other  interfaces.  This  has  recently  been  pointed  out 
by  Lorant;^  for  example,  in  comparing  the  tensions 
exhibited  by  various  liquids  in  contact  with  air  and  with 
water,  respectively,  Lorant  finds  the  following: 

S.T.  of  CHCVwater  is  about  6%-4%>S.T.  of  CHCVair 

S.T.  of  CCVwater  is  about  65%>S.T.  of  CCVair 

S.T.  of  CeHe/water  is  about  33%>ST.  of  CeHe/air   • 

S.T.  of  CeHsNO^/water  is  about  4i-42%<  S.T.  of  CeHsNO^/air 

S.T.  of  CeHnOH/water  is  about  77%<  S.T.  of  CeHxxOH/air 

Lorant  also  made  observations  on  the  surface- 
tensions  between  various  organic  fluids  (e.g.,  ether)  and 
salt  solutions.  Usually  the  influence  of  neutral  salts  on 
surface-tension  was  in  the  direction  of  an  increase.  Of 
the  different  anions  CI  has  the  greatest  effect,  and  I  and 

^Lorant,  Arch.  ges.  Physiol.,  CLVII  (1914),  211. 


LIPOID-ALTERANT  SUBSTANCES  201 

CNS  the  least;  with  ethyl  ether  and  nitromcthane,  the 
chlorides,  sulphates,  and  bromides  increased  the  intcr- 
facial  tension,  while  the  iodides  and  ihiocyanates 
decreased  it.  Similar  conditions  were  found  with 
CHCI3  and  CCI4,  but  in  this  case  iodide  also  somewhat 
increased  the  surface-tension. 

It  would  appear  that  the  physical  relations  (of 
adhesion,  mutual  solubility,  etc.)  between  water  and 
the  organic  compound,  as  well  as  between  the  latter  and 
the  non-aqueous  protoplasmic  phase  or  structure  (e.g., 
membrane)  are  of  importance  in  the  physiological  efTect. 
According  to  Traube  the  narcotic  action  of  organic 
compounds  is  determined  by  what  he  calls  their  ''Haft- 
druck"  C' adhesion- tension"),  i.e.,  special  attraction  to 
or  affinity  for  water ;^  the  tendency  of  any  compound 
to  pass  out  of  aqueous  solution  and  concentrate  in  the 
surface  layer  between  water  and  the  other  phase — i.e.,  to 
undergo  adsorption — is  in  general  the  greater  the  less 
its  affinity  for  water.  This  is  one  manner  of  interpreting 
the  relation  noted  by  Richet  and  others  between  water- 
insolubility  and  narcotic  action;  but  since  solubility  in 
water  and  solubility  in  organic  solvents — e.g.,  in  the 
esters  of  higher  fatty  acids  which  form  the  organic  sol- 
vents of  protoplasm — have  similarly  reciprocal  relations, 
this  consideration  does  not  enable  us  to  decide  whether  a 
solution-effect  or  an  adsorption-effect  is  the  essential  fac- 
tor in  the  physiological  action.  The  recent  investigations 
of  Langmuir  and  Harkins  on  adsorption^  indicate,  how- 

^  Cf.  Traube,  "Theorie  des  Haftdnicks  und  Lipoid thcoric,"  Bio- 
chem.  Zeitschrift,  LIV  (19 13),  305. 

'Langmuir,  Journal  of  the  American  Chemical  Society,  XXXIX 
(1917),  1848;  XL  (1918),  1361;  Harkins,  Clark,  and  Roberts, /6/t/.,XLI I 
(1920),  700;   Harkins  and  Cheng,  ibid.,  XLHI  (192 1),  35. 


202  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

ever,  that  there  is  no  fundamental  difference  between 
these  two  processes ;  the  affinity  for  water  seems  depend- 
ent usually  on  the  terminal  or  polar  group  of  the  organic 
compound  (COOH,  NH2,  OH,  etc.),  and  an  adsorbed 
compound  may  be  one  in  which  part  of  the  molecule  has 
an  affinity  for  (equivalent  to  solubility  in)  water,  while 
the  other  part  has  not,  but  is  attracted  more  strongly  by 
the  other  phase.  In  such  cases  the  position  at  an  inter- 
face may  be  the  chief  position  of  equilibrium,  and  the 
predominant  effect  may  be  adsorption,  with  limited  solu- 
tion in  either  phase.  Such  a  view  implies  that  the  tran- 
sition from  adsorption  to  partition  is  a  continuous  one, 
and  explains  why  highly  surface-active  compounds  usually 
have  high  lipoid-water  partition-coefficients.  Such  com- 
pounds will  enter  into  solution  in  the  non-aqueous  phase, 
provided  this  is  also  a  solvent.  They  may,  however,  con- 
dense at  the  surface  of  material  in  which  they  do  not  dis- 
solve, and  in  so  doing  influence  chemical  action  at  such 
surfaces.  Traube  calls  attention  to  the  fact  that  the  cat- 
alytic action  of  finely  divided  non-solvent  materials  like 
carbon  and  platinum  may  be  thus  influenced;  and  he 
places  narcotics  in  the  class  of  ''anti-catalysers'';^  i.e., 
they  are  regarded  as  decreasing  the  catalytic  and  hence 
the  chemical  activity  of  living  matter  by  some  form  of 
surface-action,  e.g.,  by  occupying  the  interfacial  positions 
(where  chemical  activity  appears  to  be  greatest)  in  the 
heterogeneous  protoplasmic  system  and  displacing  the 
chemically  reactive  compounds.^  This  view,  while 
partial,  may  well  be  correct  in  certain  cases,  although  it 

^  "tJber  Katalyse,"  Arch.  ges.  Physiol.,  CLIII  (1913),  309. 

*  Compare  Warburg,  Biochem.  Zeitschrift,  CXIX  (1921),  134;  see 
footnote,  p.  206. 


LIPOID-ALTERANT  SUBSTANCES  203 

probably  does  not  cover  the  entire  range  of  phenomena 
included  under  narcosis. 

INFLUENCE  OF  ORGANIC  NARCOTICS  ON  THE 
,  CHEMICAL  REACTIONS  IN  PROTOPLASM 

The  fact  that  narcotic  compounds  arrest  spontaneous 
activity,  and  in  general  act  as  depressants  of  vital 
processes  and  of  irritability,  shows  that  they  interfere 
with  the  energy-yielding  chemical  reactions  of  proto- 
plasm. The  essential  problem  relates  to  the  means  by 
which  this  effect  is  produced,  whether  it  is  primary  or 
secondary;  i.e.,  there  are  the  alternative  possibilities: 
(i)  that  the  primary  action  may  be  a  modification  of  the 
structural  conditions  on  which  the  chemical  reactions 
depend;  and  (2)  that  the  reactions  themselves  may  be  in- 
fluenced directly;  e.g.,  by  some  form  of  anticatalytic  action. 

Warburg  and  his  associates  have  made  an  extensi\'e 
study  of  the  influence  of  narcotizing  compounds  on  the 
oxygen  consumption  of  Hving  cells,  and  the  results  of 
this  work  show  many  striking  parallels  with  those  already 
described.  The  cells  used  in  the  various  determinations 
included  sea-urchin  eggs,  erythrocytes  (chiefly  of  birds), 
yeast,  lymphocytes  (from  thymus),  spermatozoa  (of 
fishes),  liver  cells  (of  frog  and  mouse),  and  bacteria 
(Vibrio,  Staphylococcus,  Bacillus  TypJii).^  In  all  cases 
the  rate  of  oxygen  consumption  was  decreased,  reversibly, 
in  the  presence  of  a  sufficient  concentration  of  anaesthetic. 
The  facts  point  in  general  to  some  kind  of  i)hysical  rather 
than  specifically  chemical  interference  with  the  oxidation 
reactions.  Thus  the  effect  produced  by  a  particular 
compound   is   largely   independent   of    the    chemically 

^  For  a  summary  of  this  earlier  work  of  Warburg,  see  Miinch.  med. 
Wochenschr.,  LVIII  (191 1),  289;   also  Warburg  and  Wiesel,  loc.  cit. 


204   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

characterizing  group;  e.g.,  two  nitriles  may  be  of  very 
unequal  effectiveness — require  different  concentrations 
to  produce  the  same  degree  of  depression,  although 
possessing  the  same  polar  group — and  the  same  is  true 
of  other  compounds.  In  any  series  the  depressant 
action  on  oxidation  is  greater  with  the  higher  members 
of  the  group;  and  the  relative  effectiveness  of  the 
different  compounds  is  closely  similar  to  that  observed 
in  experiments  on  narcosis.  For  example,  the  several 
alcohols  were  found  to  lower  the  oxygen  consumption 
of  birds'  erythrocytes  by  about  50  per  cent  in  solutions 
of  the  following  concentrations;^  Overton's  determina- 
tions of  the  minimal  anaesthetizing  concentrations  of  the 
same  compounds  for  tadpoles^  are  cited  for  comparison: 

Concentration  of  Solutions    Concentrations  (Molecular) 


Depressing 

0 

2  CONSUMP- 

Required  for  An^sthesla 

Alcohol 

tion  by 

50% 

OF  Tadpoles 

By  weight 

Molecular 

Methyl 

16 

5m 

0.52-0.62  m 

Ethyl 

7.3 

1.6  m 

0.27-0.31  m 

Propyl 

5 

0.8  m 

o.ii  m 

N-butyl 

I.I 

0.15  m 

0.038  m 

I-butyl 

I.I 

0.15  m 

0.045  ni 

Amyl 

0.4 

0.045  ^ 

0.023  m 

As  an  example  of  experiments  with  bacteria  {Vibrio 
Metschnikovii)  the  following  series  may  be  cited;  to 
diminish  oxygen  consumption  by  about  half  the  following 
concentrations  of  urethanes  were  required : 

Methyl  urethane 0.67  m  (5%) 

Ethyl 0.4111(3.5%) 

Propyl 0.097  m  (1%) 

Isobutyl 0.043  m  (o.  5%) 

Phenyl 0.003  ^^  (o-05%) 

^  Z.  physiol.  Chem.,  LXIX  (1910),  452. 
^  Studien  ilher  die  Narkose,  p.  loi. 


LIPOID-ALTERANT  SUBSTANCES  205 

The  relative  effects  of  these  compounds  on  the  anaer- 
obic growth  of  yeast  were  simihir;  the  following  solutions 
produced  about  the  same  degree  of  inhibition : 

Methyl  urethane 8% 

Ethyl  urethane 4% 

Propyl  urethane 2% 

Isobutyl  urethane 1% 

Phenyl  urethane 0.1% 

These  results^   are  similar   to   those  of  Regnard   with 
alcohols,  cited  above. 

Usui,  working  under  Warburg's  direction,^  found  also 
a  decrease  in  the  oxygen  consumption  of  vertebrate 
tissues  (liver,  central  nervous  system)  under  the  influence 
of  narcotic  compounds  (alcohols,  ketones,  urethanes, 
methyl  urea,  and  phenyl  urea) ;  but  in  order  to  produce 
marked  depression  of  oxidations  much  higher  concentra- 
tions were  required  than  in  normal  reversible  narcosis, 
and  the  effect  was  imperfectly  reversible.  This  result 
is  interesting  as  indicating  that  anaesthesia  is  not  neces- 
sarily associated  with  a  decrease  of  intracellular  oxida- 
tions, as  Verworn  and  others  have  supposed;  in  fact, 
Warburg,  Winterstein,  Loeb  and  Wasteneys,  and  others 
have  shown  in  a  number  of  instances  that  anaesthesia 
when  perfectly  reversible  does  not  necessarily  involve 
a  decrease  in  oxygen  consumption.^  Diminished  oxida- 
tion is  to  be  regarded  rather  as  a  secondary  consequence 
than  as  a  cause  of  narcosis.     Apparently  the  chemical 

^  Warburg  and  Wiesel,  loc.  cit. 

2  Usui,  Arch.  ges.  Physiol,  CXLVII  (1912),  100. 

3  Warburg,  Z.  physiol  Chem.,  LXVI  (1910),  305;  LXX  (191 1), 
413;  Winterstein,  Biochem.  Z.,  LXI  (1914),  81;  also  Wintcrstcin's 
book  on  narcosis;  Loeb  and  Wasteneys,  Journal  of  Biological  Chemistry, 
XIV  (1913),  517;  Biochem.  Zeitschrift,  LVI  (1913)1  295- 


2o6    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

effect  is  secondary  to  some  physical  modification  pro- 
duced in  the  protoplasm  by  the  narcotizing  compound.^ 

PHYSICAL  CHANGES  PRODUCED  BY  LIPODD-SOLVENT 
COMPOUNDS  IN  PROTOPLASM 

Certain  definite  changes  in  the  physical  properties  of 
protoplasm,  analogous  in  many  respects  with  those 
produced  by  salts,  have  been  observed  in  various  cases 
to  accompany  the  action  of  narcotizing  compounds; 
these  changes  indicate  that  underlying  narcosis  there 
are  definite  modifications  of  the  structural  conditions  in 
protoplasm;  and  presumably  it  is  to  such  modifications 
that  the  changes  in  physiological  properties  and  activity 
are  to  be  referred.  As  we  have  seen,  the  distinctively 
vital  processes  are  controlled  by  structural  conditions; 
structural  change  impHes  physiological  change. 

'  For  a  more  detailed  discussion  of  the  relation  of  narcosis  to  oxida- 
tion processes  see  my  review,  "The  Theory  of  Anaesthesia"  {Biological 
Bulletin,  XXX  (1916),  311,  also  American  Yearbook  of  Anaesthesia,  I,  i). 

According  to  Warburg  (cf .  his  recent  article  on  the  physical  chemistry 
of  cell-respiration,  Biochem.  Zeitschrijt,  CXIX  [1921],  134)  the  proto- 
plasmic oxidations  occur  at  the  surface  of  the  solid  cell  structures,  which 
adsorb  the  water-soluble  oxidizable  compounds;  narcotics  influence 
oxidations  by  changing  the  physical  and  chemical  character  of  the  surfaces. 

He  expresses  his  general  conclusions  on  the  conditions  of  proto- 
plasmic oxidations  as  follows:  "Two  chief  means  are  employed  by  the 
cell  to  diminish  the  chemical  resistance  at  the  regions  of  oxidation; 
namely,  adsorption  and  the  catalytic  action  of  heavy  metals  ....  Cell 
respiration  is  a  capillary  process  occurring  at  the  iron-containing  surfaces 
of  the  solid  cell-constituents.  By  adsorption  at  these  surfaces  the  inert 
organic  compounds  become  capable  of  reacting  with  O2  just  as  do  amino- 
acids  at  the  surface  of  charcoal.  This  view  does  not  explain  respiration 
in  the  physical  sense,  but  classes  it  with  general  phenomena  of  the 

inorganic  world Narcotics  check  the  cell-oxidations  by  occupying 

the  surfaces  and  thereby  displacing  the  oxidizable  compounds.  The  same 
action  is  exhibited  by  dififerent  narcotics  when  the  same  fraction  of  the 
active  surface  is  occupied  by  the  narcotic"  (pp.  152,  153). 


LIPOID-ALTERANT  SUBSTA^XES  207 

Changes  of  permeability,  of  viscosity,  and  of  resist- 
ance to  the  action  of  cytolytic  or  other  injurious  condi- 
tions are  the  most  evident  physical  elTects  produced  by 
lipoid-alterant  compounds  in  living  protoplasm.  During 
narcosis  there  appears  very  generally  to  be  a  decrease  of 
permeabiHty,  an  increase  in  the  resistance  to  structural 
breakdown  or  cytolysis,  and  an  increase  of  protoplasmic 
viscosity.  From  the  general  nature  of  these  changes  it 
would  seem  that  the  structural  substratum  of  the  living 
matter  assumes  temporarily  a  denser  or  physically  more 
stable  condition.  In  any  event  it  is  clear  that  the 
modification  is  in  such  a  direction  as  to  interfere  with 
stimulation,  a  process,  which  (as  we  shall  see  later) 
involves  structural  changes  in  the  irritable  system. 
Hence  what  may  be  described  as  a  stabilization ,  decrease 
of  susceptibiHty  to  structural  change,  is  indicated  as  in 
all  probabiHty  the  essential  physical  condition  underlying 
narcosis;  but  any  such  general  term  gives  little  indication 
of  the  detailed  nature  of  the  physical  modification 
produced  in  the  Hving  protoplasm.  The  manner  in 
which  narcosis  modifies  stimulation-processes  will  be 
considered  in  more  detail  later;  in  the  present  section 
we  shall  merely  describe  briefly  those  changes  in  the 
physical  state  of  protoplasm  which  appear  to  ha\e  some 
bearing  on  the  question  of  the  nature  of  the  conditions 
determining  narcosis. 

The  changes  observed  in  the  larva  of  Arcnicola  arc 
simple  and  instructive;  normal  larva)  transferred  from 
sea  water  to  pure  isotonic  NaCl  solution  undergo  stimula- 
tion and  marked  increase  of  permeabiHty  as  shown  by 
loss  of  pigment;  on  the  other  hand,  larva?  which  arc 
first  placed  in  a  solution  of  a  magnesium  salt,  or  in  sea 


2o8    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

water  containing  a  suitable  anaesthetic  (ether,  chloretone, 
alcohol)  in  the  narcotizing  concentration,  and  are  then 
transferred  to  NaCl  solution  (preferably  containing 
anaesthetic),  show  no  such  effect;  there  is  no  immediate 
loss  of  pigment  and  little  or  no  stimulation.  The 
breakdown  of  ciHa  in  the  NaCl  solution  is  also  prevented/ 
A  protective  (antitoxic)  or  stabilizing  action  is  associated 
with  the  narcotizing  action  in  this  organism;  and 
essentially  similar  conditions  have  been  found  in  the 
eggs  of  the  sea-urchin  Arhacia.^  Analogous  observations 
have  been  made  on  other  cells  by  a  number  of  investiga- 
tors. Arrhenius  and  Bubanovic  found  that  the  break- 
down of  blood  corpuscles  in  hypotonic  media  was 
hindered  by  anaesthetics;^  similar  observations  have  more 
recently  been  made  by  Linzenmeier  and  Runnstrom; 
haemolysis  and  agglutination  by  foreign  proteins  may 
also  be  diminished  by  anaesthetics."*  These  "stabiliza- 
tion" effects  are  observed  in  the  concentrations  corre- 
sponding to  the  anaesthetizing  range;   higher  concentra- 

'R.  S.  Lillie,  American  Journal  of  Physiology,  XXIX  (1912),  372; 
XXXI  (1913),  255. 

^  R.  S.  Lillie,  American  Journal  of  Physiology,  XXX  (19 12),  i. 

3  Publications  of  Nobel  Institute  (1913),  No.  32,  cited  from  Hober's 
Physikalische  Chemie  der  Zelle  u.  der  Gewebe,  p.  466. 

4  See  Linzenmeier,  Arch.  ges.  Physiol.,  CLXXXI  (1920),  169,  and 
CLXXXVI  (1921),  272;  for  similar  observations  on  bacteria  cf.  Vor- 
schiitz,  ibid.,  CLXXXVI  (1921),  290;  Runnstrom,  Biochem.  Zeitschrift, 
CXXIII  (1921),  I.  See  also  the  observations  of  Traube  {Biochem. 
Zeitschrift,  X  [1908J,  371)  and  Clowes  {Proceedings  of  the  Society  of  Experi- 
mental Biology  and  Medicine,  XI  [1913],  8).  These  changes  of  properties 
resulting  from  the  modification  of  surface-films  have  an  interesting 
relation  to  those  produced  by  addition  of  proteins  to  suspensions  of 
bacteria  and  blood  corpuscles,  and  recently  investigated  by  Northrop 
and  de  Kruif  {Jour.  Gen.  Physiol.,  IV  [1922],  655),  Eggerth  and  Bellows 
{ibid.,  p.  669),  and  Coulter  {ibid.,  p.  403). 


LIPOID-ALTERANT  SUBSTANCES  209 

tions  produce  irreversible  structural  chanj^^e  or  cytolysis. 
Such  facts  indicate,  in  general,  that  in  the  narcotizing 
solutions  the  plasma  membranes  become  more  resistant 
to  alteration.  Hober's  observations  on  the  action  of 
anaesthetics  in  hindering  the  production  of  injury- 
currents  in  muscle  by  potassium  salts  illustrate  the  same 
condition;  the  local  negativity  (an  index  of  increase  of 
permeability)  develops  much  more  slowly  in  the  presence 
of  ether,  urethane,  and  other  narcotizing  compounds 
than  in  the  pure  solution.^ 

A  decrease  of  permeability  to  water-soluble  diffusing 
substances  and  ions,  and  also  in  some  cases  to  water,  is 
an  effect  of  a  related  kind.  The  entrance  of  water- 
soluble  dyes  into  plant  cells  {Spirogyra)  is  retarded 
during  anaesthesia;^  neutral  salts  may  also  produce 
this  effect  both  in  animal  and  plant  cells.^  Decreased 
permeability  to  ions  is  indicated  by  decreased  electrical 
conductivity;  this  has  been  demonstrated  by  Osterhout 
in  Laminaria,  by  McClendon  in  sea-urchin  eggs,  and  by 
Joel  in  blood  corpuscles."*  In  Laminaria  a  reversible 
decrease  of  conductivity  is  found  only  in  moderate 
concentrations  of  ether  and  other  anaesthetics,  corre- 
sponding to  the  anaesthetizing  concentrations;  stronger 
solutions    cause    marked    and    irreversible    increase    of 

^Hober,  Arch.  ges.  Physiol.,  CVI  (1905),  599. 
2  Lepeschkin,  Ber.  deulsch.  hotan.  Ges.,  XXIX  (1911),  349- 
3Szucs,  Jahrh.  wiss.  Botanik,  LII  (191 2),  85.     Cf.  also  the  recent 
observations  by  Miss  Irwin,  Jour.  Gen.  Physiol,  V  (i9-^3)>   =23,  727. 
Mg  salts  decrease  the  rate  of  penetration  of  dyes  into  ArenicoJa  larvae 
(American  Journal  of  Physiology,  XXIV  [1909].  26). 

4 Osterhout,  Science,  XXXVII  (1913),  m;  ^^'^  ^^^"^  "''''■'^'  ^^'^ 
(1913),  129;  McClendon,  Popular  Scientific  Monthly  (1915),  P-  5^9;  »"<! 
Joel,  Arch.  ges.  Physiol.,  CLXI  (1915),  5- 


2IO   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

conductivity,  indicating  a  destructive  or  cytolytic  effect. 
In  fertilized  sea-urchin  eggs,  anaesthetics  (chloral, 
hydrate,  alcohols,  urethane)  decrease  the  permeability 
to  water,  as  shown  by  the  decreased  rate  of  shrinkage 
in  hypertonic  sea  water  containing  the  anaesthetizing 
compound.'  The  penetration  of  acids  into  the  pigment- 
containing  mantle  cells  of  nudibranchs  is  also  retarded 
by  anaesthetics.^ 

Changes  of  protoplasmic  viscosity,  as  indicated  by 
changes  in  the  readiness  with  which  cell  structures  are 
mechanically  displaced  (by  centrif uging) ,  have  also  been 
observed,  but  the  character  of  the  change  appears  to 
vary  in  different  forms  of  protoplasm.  In  plant  cells, 
according  to  the  observations  of  Heilbronn^  on  seedhngs 
and  F.  Weber^  on  Spirogyra,  ether  in  the  anaesthetizing 
concentrations  increases  the  viscosity  of  the  protoplasm; 
in  lower  concentrations,  on  the  other  hand,  it  decreases 
viscosity.  This  result  agrees  with  the  observations 
of  Ewart^  and  others  who  find  that  weak  solutions  of 
anaesthetics  accelerate  protoplasmic  streaming  while 
stronger  solutions  retard  or  arrest  it.  In  sea-urchin 
eggs  L.  Heilbrunn^  has  recently  found  that  various 
anaesthetics  in  concentrations  sufficient  to  prevent  cell- 

^  R.  S.  Lillie,  American  Journal  of  Physiology,  XLV  (191 8),  406; 
cf.  p.  427. 

'  Crozier,  Jour.  Gen.  Physiol.,  IV  (1922),  723. 
3Heilbronn,  Jahrb.  wiss.  Botanik,  XLIV  (1914),  357. 

4F.  Weber,  Biochem.  Zeitschrift,  CXXVI  (192 1),  21;  Ber.  deutsch. 
hotan.  Ges.y  XL  (1922),  212. 

s  Ewart,  O71  the  Physiology  and  Physics  of  Protoplasmic  Streaming  in 
Plants,  Oxford  (1903).  Cf.  also  the  observations  by  Demoor  and  others 
cited  in  Czapek's  Biochemie  der  Pflanzen,  Jena  (1913),  p.  161. 

^L  Heilbrunn,  Biological  Bulletin,  XXXIX  (1920),  307. 


LIPOID-ALTERANT  SUBSTANCES  211 

division  cause  decrease  of  viscosity,  i.e.,  facilitate  the 
displacement  of  granules  by  the  centrifuge.  In  some 
cases,  however,  Heilbrunn  found  effects  of  the  opposite 
kind;  and  he  distinguishes  two  kinds  of  ana,'sthesia,  in 
which  protoplasmic  viscosity  is  respectively  increased 
and  decreased.  The  significance  of  such  changes  in 
relation  to  the  functional  activity  of  the  cell  is  not  clear. 
They  show,  however,  that  the  structural  conditions 
within  the  protoplasmic  system  are  modified  reversibly 
by  the  lipoid-solvent  group  of  compounds  and  that  the 
concentrations  required  for  this  effect  correspond  to 
those  which  produce  narcosis. 

Apparently  the  most  general  inference  to  be  drawn 
from  the  foregoing  facts  is  that  one  constant  accomi)ani- 
ment  of  narcosis  is  a  modification,  in  the  direction  of 
greater  stability  or  impermeability,  of  the  physical  state  of 
the  plasma  membrane  of  the  irritable  cells;  and  there  is 
good  reason  to  beheve  that  the  physiological  effect  of 
narcotic  compounds  depends  on  this  effect;  this  conclusion 
will  receive  further  support  when  the  subject  of  stimula- 
tion is  discussed.  The  chief  locus  of  action  of  anaesthetics 
thus  appears  to  be  the  same  as  that  of  salts,  which  is 
evidently  superficial,  as  already  pointed  out.  Antago- 
nisms between  salt  action  and  aucTsthctic  action  are  in 
fact  readily  demonstrable  in  many  cases. ^  Salts  like 
NaCl  in  pure  solution  tend  to  disintegrate  the  plasma 
membranes,  and  the  addition  of  an  aniesthetizing 
compound  to  the  solution  frequently  retards  or  prevents 

^  See  my  series  of  papers  on  antagonisms  between  salts  and  anes- 
thetics, American  Journal  of  Physiology,  XXIX  (191 2),  372;  XXX,  i, 
and  XXXI  (1913),  255;  dlso  Journal  of  Experimental  Zoology,  XVI  (1914), 
591.  Hober's  observations  (above  cited)  on  the  ctTects  of  anesthetics 
in  retarding  the  production  of  injury-currents  in  muscle  by  salts  furnish 
other  examples  of  this  phenomenon. 


212    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

this  action  in  a  manner  resembling  that  of  an  antagonistic 
salt  like  CaCla.  Clowes  has  shown  that  in  the  physical 
drop-systems  which  he  studied — alkaline  NaCl  solution 
flowing  from  a  stalagmometer  through  oil — anaesthetics 
produce  an  effect  closely  comparable  with  that  of  CaCla; 
both  actions  are  to  be  referred  to  changes  in  the  properties 
of  the  interfacial  films  formed  between  the  oil  and  the 
aqueous  solution/  The  presence  of  a  compound  (Ca 
soap,  or  fat-solvent  compound)  which  is  more  soluble 
in  the  oil  phase  than  in  the  water  phase,  modifies  the 
conditions  at  the  boundary  in  the  same  manner  in  both 
cases,  and  produces  the  same  physical  effect  in  the 
system.  The  parallelisms  observed  by  Clowes  between 
the  biological  and  the  physical  phenomena  may  be 
interpreted  as  indicating  that  the  conditions  in  living 
protoplasm  are  of  a  closely  analogous  kind. 

The  foregoing  effects  of  anaesthetics  on  the  physical 
properties  of  protoplasm  do  not,  however,  enable  us  to 
decide  whether  the  solvent  action  or  the  adsorbent 
action  is  the  chief  factor  in  the  narcotic  effect,  or  whether 
both  are  equally  concerned.  Certain  widely  general 
biological  phenomena  do  not  appear  to  be  entirely 
consistent  with  Traube's  theory  that  surface-activity  is 
the  essential  factor  in  all  cases  of  narcosis.  These  are: 
(i)  the  great  differences  observed  between  the  narcotizing 
concentrations  of  the  same  compound  in  different  cells, 
tissues,  and  organisms;  (2)  the  fact  that  weak  solutions 
of  many  narcotic  compounds  have  a  sensitizing  or 
accelerating  influence  on  many  cell-processes;^    (3)  the 

'  Clowes,  Journal  of  Physical  Chemistry,  XX  (19 16),  407;  cf. 
pp.  434  ff- 

2  Cf.  the  instances  cited  in  my  review  of  the  theory  of  anaesthesia 
{Biological  Bulletin,  loc.  cit.). 


LIPOID-ALTERANT  SUBSTA.NCKS  213 

general  relation,  pointed  out  by  Overton  and  Meyer, 
between  the  lipoid-content  of  tissues  and  their  suscej)ti- 
bihty  to  narcotic  action;  and  (4)  the  ana'sthetizing  action 
of  compounds,  such  as  Mg  and  K  salts,  which  are  without 
surface-activity  in  the  foregoing  sense.  Traube's  theory 
in  fact,  in  emphasizing  the  importance  of  a  single  })hysical 
factor,  seems  to  disregard  other  possible  factors,  and  on 
the  whole  to  underestimate  the  complexity  of  the 
physiological  conditions. 

Hober,^  Vernon,^  and  others  have  pointed  out 
various  exceptions  to  the  rule  that  isocapillary  solutions 
have  equal  physiological  action.  Tliis  rule  cannot  be  true 
in  any  precise  sense,  since  an  organic  compound  may 
affect  the  conditions  at  the  various  interfaces  in  a  complex 
system  Kke  protoplasm,  and  at  an  air- water  interface, 
quite  differently;  and  other  factors,  incluchng  viscosity, 
solubihty  in  the  protoplasmic  phases,  and  specific 
chemical  affinities  enter  to  modify  the  simple  surface 
conditions.  In  cases  where  the  conditions  are  simple, 
the  increase  from  compound  to  compound  in  a  homolo- 
gous series  may  be  very  regular;  a  good  example  is 
seen  in  FUhner's  observations  on  haemolysis  by  solutions 
of  alcohols;^  the  critical  hcTmolytic  concentrations  for 
the  first  five  alcohols  are  as  follows : 

m.-sol. 

Methyl 7-34 

Ethyl 3-24 

Propyl I  ■  08 

Butyl 0.312 

Amyl o .  09 

^  Hober,  Physik.  Chan.  d.  Zelle,  p.  415- 
2  Vernon,  Biochem.  Zeitschrift,  LI  (19 13),  i. 

3Fuhner  and  Neubauer,  Arch,    expcr.    Path.   n.   PharmakcL,   lAI 
1907);  2>32,- 


214    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

In  this  case,  the  ratio  of  about  3 :  i  between  successive 
members  is  well  shown.  In  other  cases  this  relation  is 
obscured  by  chemical  and  other  factors;  an  instructive 
instance  is  the  relatively  high  toxicity  of  methyl  as 
compared  with  ethyl  alcohol,  apparently  a  consequence 
of  the  special  properties  of  the  former's  oxidation 
products,  formaldehyde  and  formic  acid.  Fiihner  cites 
other  cases  showing  a  similar  regularity;  he  finds, 
however,  that  in  tissues  with  high  Hpoid-content,  such 
as  the  vertebrate  central  nervous  system,  the  higher 
members  of  certain  series  (alcohols)  are  more  effective 
than  would  be  expected  from  this  simple  rule.  This 
discrepancy  he  ascribes  to  the  larger  proportion  of 
organic  solvent  (Kpoid)  in  such  tissues;  thus,  in  the 
adult  frog  the  divergence  from  the  3 :  i  ratio  is  greater 
{  =  ca,  4:1)  than  in  the  tadpole  (  =  2.9:1);  this  difference 
is  apparently  referable  to  the  increase  in  lipoid  constitu- 
ents as  the  central  nervous  system  develops.^  It  seems 
probable  that  in  Hpoid-rich  tissues  the  Upoid-solvent 
factor  becomes  relatively  important  in  comparison  with 
the  capillary  constant  factor. 

The  relatively  great  solubility  of  many  anaesthetic 
organic  compounds  in  protein-containing  systems  defi- 
cient in  Hpoid  (serum,  finely  divided  muscle,  etc.)  has 
been  attributed  by  Moore  and  Roaf^  to  the  formation 
of  chemical  combinations  with  the  protein;  but  since 
all  such  systems  are  undoubtedly  polyphasic,  and  since 
chemical  combinations  (in  the  stoichiometric  sense)  of 
hydrocarbons  (Hke  CHCI3,  benzol,  etc.)  with  proteins  are 

^  Fiihner,  Z.  Biol.,  LVII  (191 2),  465. 

=*  Moore  and  Roaf,  Proceedings  of  the  Royal  Society,  B,  LXXIV 
(1908),  382;  LXXVII  (1906),  86. 


LIPOID-ALTERANT  SUBST ANTES  215 

difficult  to  conceive,  it  seems  more  likely  that  an 
adsorption-effect  is  involved,  similar  to  that  observed 
in  finely  divided  suspensions  of  charcoal.  It  is  well 
known  that  the  catalytic  effect  of  such  suspensions  is 
markedly  influenced  by  surface-active  compounds;'  this 
effect  indicates  an  alteration  in  the  character  of  the 
surface,  probably  resulting  from  adsorption.  Other 
phenomena  of  a  related  kind,  e.g.,  the  precipitation 
produced  by  organic  solvents  in  protein  solutions  (as 
observed  by  Battelli  and  Stern  and  Moore  and  Roaf),' 
the  liquefying  action  of  these  compounds  on  gelatine 
gels  (Traube  and  Kohler),^  the  soUdifying  action  on 
lecithin  suspensions,  and  the  interference  with  the 
precipitation  of  lecithin  suspensions  by  electrolytes 
(Koch,  Hober  and  Gordon,  and  others),-'  are  similarly 
referable  to  surface-conditions,  although  the  special 
nature  of  these  conditions  is  not  clear  in  all  cases.  It 
is  noteworthy  that  most  of  these  effects  are  obser\'ed 
at  concentrations  far  in  excess  of  those  required  to 
produce  reversible  narcotic  effects  in  living  protoplasm. 
To  characterize  the  organic  anaesthetics  as  negative 
catalyzers,  as  Traube  does,  may  place  them  in  a  class, 
but  does  not  explain  their  characteristic  action  on 
living  matter. 

It  seems  certain  from  the  physical  peculiarities  of 
these  substances  that  they  must  undergo  adsorjDtion 

»  Cf.  Warburg,  Arch.  ges.  Physiol.,  CLV  (1914),  547- 

2  Battelli  and  Stern,  Biochem.  Zeilschrift,lAl  (1913),  226;  Moore 
and  Roaf,  loc.  cit. 

3  Traube  and  Kohler,  Intcrnat.  Zcitschr.  f.  physik.-chan.  Biol.,  II 
(1915),  42. 

4  Cf.  pp.  360  fif.  of  my  Theory  of  Anesthesia,  loc.  cit. 


2i6    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

at  the  structural  surfaces  in  protoplasm,  and  also  dissolve, 
in  accordance  with  their  partition- coefficients,  in  the 
organic  solvents  of  protoplasm.  It  is  not  a  case  of  two 
incompatible  processes;  both  occur  simultaneously,  and 
each  contributes  to  the  total  effect.  Possibly  the 
reversible  effects  characteristic  of  low  concentrations  of 
anaesthetic  substances  are  the  expression  of  solution  in 
the  lipoids,  while  with  higher  concentrations  the  specific 
structural  compounds  of  the  protoplasm,  the  proteins, 
are  affected  through  coagulation  or  other  changes  due 
to  adsorption,  and  irreversible  effects  result.  The 
reversible  effects — stimulation  or  sensitization  in  very 
weak,  inhibition  or  anaesthesia  in  stronger,  solutions — 
are  the  expressions,  respectively,  of  facilitation  and 
hindrance  of  the  normal  metabolic  processes  underlying 
stimulation  and  automatic  activity;  i.e.,  the  influence 
of  the  cell-structure  on  the  metaboUc  reactions  is  modi- 
fied, and  the  whole  behavior  of  the  protoplasmic  system 
is  altered  correspondingly. 

If  the  influence  of  structural  conditions  on  cell- 
metabolism  is  to  be  included  under  the  class  of  heterogene- 
ous or  contact  catalysis,  as  many  of  the  foregoing  facts 
indicate,  it  is  evident  that  a  consideration  of  this  type 
of  catalysis  and  of  the  manner  in  which  it  is  influenced 
by  substances  of  the  foregoing  kind  becomes  essential  in 
the  further  analysis  of  the  conditions  in  living  protoplasm. 


CHAPTER  X 

CATALYSIS  IN  RELATION  TO  THE  CHEMICWL 
PROCESSES  IN  LIVING  MAITER 

The  chemical  reactions  in  protoplasm  are  under  the 
control  of  structure,  as  we  have  seen,  and  their  velocity 
is  decreased  and,  in  the  case  of  the  most  characteristically 
vital  reactions,  the  specific  syntheses,  is  reduced  to  zero 
when  protoplasmic  structure  is  destroyed.  If  we  class 
this  influence  of  structure  as  catalysis,  the  case  becomes 
one  of  heterogeneous  catalysis,  in  which  the  reacting 
substances  are  predominantly  substances  in  aqueous 
solution.  Organic  solvents,  however,  are  also  present, 
represented  chiefly  by  the  lipoids;  and,  as  in  all  cases  of 
heterogeneous  catalysis,  the  interfacial  relations  are 
undoubtedly  of  primary  importance.  The  permanent 
structural  elements  are  chiefly  protein  in  composition, 
probably  associated  with  lipoid;  and  this  fact  favors  the 
inference  that  the  interfaces  between  the  soUd  protein 
structures  of  the  cell  and  the  adjoining  more  fluid  ])hases 
are  the  site  of  the  biologically  essential  reactions,  and 
especially  of  the  syntheses.  The  fact  that  surface- 
active  substances  as  a  class  interfere  so  strongly  with 
these  reactions  favors  this  interpretation. 

The  distinctive  syntheses  of  living  matter  are  those 
of  proteins.  These  are  the  syntheses  on  which  specific 
growth  depends,  and  growth  is  the  fundamental  vital 
activity.  It  thus  appears  probable  that  growth  is 
chiefly  a  result  or  expression  of  synthetic  reactions 
occurring  at  such  interfaces;    and  the  general  susccpti- 

217 


2i8    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

bility  of  protoplasmic  processes,  including  growth,  to 
electrical  influences  seems  to  imply  that  the  electrical 
conditions  existing  at  these  interfaces  are  an  essential 
factor  in  the  control  of  these  reactions. 

The  general  subject  of  the  catalysis  of  substances 
in  aqueous  solution  in  heterogeneous  systems  has  thus 
an  intimate  bearing  on  the  fundamental  biological 
problem  which  we  are  considering;  and  a  brief  review 
of  the  more  relevant  facts  in  this  field  is  essential  to  the 
further  analysis  of  the  conditions  in  living  protoplasm. 
It  must  be  remembered,  however,  that  the  theory  of 
catalysis  is  still  in  many  respects  incomplete,  and  that 
many  reactions  in  living  protoplasm  appear  to  be 
determined  by  other  than  purely  catalytic  conditions — 
using  the  word  catalysis  in  the  accepted  sense  of  an 
acceleration  in  which  the  catalyzer  undergoes  no  perma- 
nent change  in  the  reaction.  Induced  reactions  probably 
play  an  important  part;  and  there  are  apparently  also 
cases  where  the  catalyzer  acts  by  introducing  a  factor 
necessary  to  those  special  physical  conditions — e.g., 
flow  of  electric  current  through  the  bioelectric  circuit — 
which  control  the  reaction. 

The  general  parallel  between  the  conditions  deter- 
mining chemical  reaction-velocities  in  general,  and  those 
determining  the  flow  of  an  electric  current  through  a 
circuit,  has  often  been  dwelt  upon.^  The  quantity  of 
material  transformed  in  a  reaction,  or  of  current  flowing 
through  the  circuit  is  determined:  (i)  by  the  intensity 
of  a  physical   condition,   called  electrical  or  chemical 

^  Cf.  Moore,  Recent  Advances  in  Physiology  and  Biochemistry^ 
pp.  45  ff.;  Mellor,  Chemical  Statics  and  Dynamics,  p.  25;  van't  Hoff,  Vor- 
lesungen,  I,  172,  178;  Bredig,  Ergehnisse  der  Physiol. .,  I  (1902),  137. 


CATALYSIS  AND  BIOCHEMICAL  PROCESSES     219 

^^potential,''  whose  expression  is  a  furtherance  of  the 
change  in  question;  and  (2)  by  the  resistance  to  this 
change.  The  general  formula  C  =  P/R  describes  the 
general  conditions,  where  C  signifies  either  the  rate  of 
chemical  change  (under  determined  conditions  of  con- 
centration, temperature,  etc.)  or  the  intensity  of  the 
current  flowing  through  the  circuit,  P  the  potential, 
signifying  a  function  of  ''chemical  affinity"  in  the  one 
case,  or  the  electrical  pressure  or  ''voltage"  of  the 
circuit  in  the  other,  and  R  the  resistance  to  either  the 
chemical  change  or  the  flow  of  current.  In  the  case  of 
a  chemical  reaction  occurring  at  an  electrode  (electroly- 
sis), where  the  quantity  of  chemical  change,  e.g.,  of 
copper  deposited  as  metal  at  the  cathode,  is  proportional 
to  the  quantity  of  current  flowing  through  the  circuit 
(Faraday's  Law),  the  factors  determining  the  flow  of 
current  are  the  same  as  those  determining  the  rate  of 
chemical  change,  and  chemical  resistance  becomes 
identical  with  electrical  resistance.  In  such  a  case  any 
condition  decreasing  the  electrical  resistance  or  increasing 
the  electrical  potential  increases  the  velocity  of  the  purely 
chemical  change  at  the  electrode. 

At  present  it  is  customary  to  describe  a  patalyst  as 
a  substance  which  in  some  manner,  without  itself  under- 
going permanent  alteration,  decreases  the  resistance 
to  the  interaction  of  other  substances  in  the  reaction- 
system.  On  such  a  definition  any  substance  which 
decreases  the  electrical  resistance  in  a  circuit  would 
catalyze  the  chemical  reactions  occurring  at  the  elec- 
trodes. Such  an  effect  might  not  ordinarily  be  classed 
as  catalytic;  but  since  our  interest  is  not  in  defining 
the  significance  to  be  attached  to  terms,  but  in  ascertain- 


220   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

ing  the  physico-chemical  conditions  under  which  chemical 
reactions  actually  are  accelerated  in  systems  of  the  kind 
under  consideration,  we  must  note  as  especially  signifi- 
cant the  fact  that  reactions  occurring  under  electrical 
influence  at  surfaces  (especially  metallic  surfaces)  may 
be  influenced  in  their  velocity  by  the  contact  of  materials 
which  change  locally  the  electrical  state  of  the  surface. 
The  rusting  of  iron  in  water  or  salt  solution  is  a  good 
instance  of  this  type  of  effect;  the  reaction  may  be 
greatly  accelerated  by  placing  another  metal,  e.g., 
copper  or  platinum  (which  itself  does  not  undergo 
change)  in  contact  with  the  iron.  The  apparently 
catalytic  effect  in  this  case  is  due  to  the  formation  of 
an  electrical  circuit  between  the  two  metals,  the  iron 
becoming  anodal  and  hence  freeing  Fe  ions  with  increased 
rapidity;  these  can  then  react  to  form  carbonate  or 
hydrate  with  the  anions  present  in  the  solution.  Another 
simple  and  striking  demonstration  of  a  ''catalytic" 
action  of  this  kind  is  made  by  placing  in  a  solution  of 
K3FeCy6  (containing  a  little  NaCl  to  allow  a  soluble 
zinc  salt  to  be  formed)  two  similar  strips  of  metallic  zinc, 
one  of  which  is  marked  with  a  lead  pencil  or  bound  with 
a  small  piece  of  copper  or  platinum,  while  the  other  is 
free  from  such  contact.  In  a  few  hours  a  luxuriant 
''growth"  of  filaments  and  tubules  of  zinc  ferricyanide 
is  formed  from  the  first  strip,  while  the  second  remains 
almost  unaltered.  The  carbon,  or  the  noble  metal, 
acts  ''catalytically"  in  this  reaction  because  it  furnishes 
a  surface  of  lower  solution-tension,  which  forms  the 
cathode  of  the  local  electric  couple;  and  since  these  two 
areas  are  in  metalHc  connection  and  immersed  in  the 
electrolyte    solution,    a    current    flows    which    enables 


CATALYSIS  AND  BIOCHEMICAL  PROCESSES     221 

Zn  ions  to  enter  the  solution  more  nii)i(lly  and  hence 
accelerates  the  formation  of  the  structure-forming  i)rf- 
cipitate  of  zinc  ferricyanide.^ 

There  is  reason  for  believing  that  the  remarkable 
chemical  activity  of  Hving  matter,  as  well  as  its  sus- 
ceptibihty  to  electrical  influence  and  to  stimuhition, 
is  largely  dependent  on  physical  conditions  which  are 
fundamentally  of  the  kind  just  described.  For  example, 
during  stimulation  the  excited  and  the  unexcited  areas 
of  the  reactive  protoplasmic  surface — the  surface  of  the 
irritable  cell,  neurofibril,  or  other  structure  concerned — 
are  at  different  electrical  potentials;  apparently  the 
current  flowing  between  these  two  areas  produces  chem- 
ical effects  which  secondarily  determine  the  propagation 
of  the  state  of  excitation  and  hence  the  distinctively 
physiological  effect  or  response.  There  is  a  close  analogy 
here  to  the  case  of  local  circuits  in  metals  immersed  in 
electrolyte  solutions;  these  circuits  also  fonn  the  con- 
dition for  the  transmission  of  chemical  effects.  Tliis 
general  condition  will  be  considered  more  fully  under 
the  subject  of  stimulation;  at  present  it  is  suflicient  to 
call  special  attention  to  it  as  probably  fonning  a  higlily 
important  factor  in  the  catalytic  or  quasi-catalytic 
action  of  Hving  protoplasm.  Here  we  use  the  term 
''catalytic"  simply  as  a  designation  for  the  remarkable 
property  shown  by  hving  protoplasm  of  enabling  reac- 
tions to  occur,  at  a  relatively  high  velocity,  which  arc 
absent  or  inappreciable  in  dead  protoplasm. 

The  most  famihar  form  of  catalysis  observed  in 
living  organisms,  and  the  one  showing  the  ch^sest  parallels 

^  Cf.  my  two  papers  on  precipitation  growtlis  from  molals,  liiolo^uai 
Bulletin,  XXXIII  (1917),  135,  and  (with  E.  N.Johnston)  XXXVI  (1919), 
225. 


222    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

with  the  usual  inorganic  types  of  catalysis,  is  that 
dependent  on  the  activity  of  enzymes.  Enzymes  are 
constant  constituents  of  protoplasm,  and  their  presence 
accounts  for  many  characteristic  features  of  its  chemical 
performance.  Enzyme-action,  however,  is  obviously 
responsible  for  only  a  portion  of  the  metaboHc  reactions, 
especially  the  destructive  or  disintegrative  ones,  which 
are  largely  hydrolytic.  Although  certain  types  of  syn- 
thesis are  accelerated  by  enzymes  under  certain  condi- 
tions (dehydrolytic  synthesis  of  esters,  carbohydrates, 
and  apparently  polypeptides),  others  cannot  be  thus 
accounted  for;  e.g.,  photosyn theses,  synthesis  of  fat 
from  protein  or  carbohydrate,  or  other  syntheses  involv- 
ing the  expenditure  of  much  energy.  Moreover,  the 
responsiveness  of  protoplasm  to  stimulation  is  not  thus 
explained,  since  enzymes  show  no  such  instantaneous 
and  marked  acceleration  of  their  action,  under  electrical 
or  mechanical  influence,  as  is  shown  by  Hving  protoplasm. 
As  we  shall  see  later,  changes  in  protoplasmic  structure 
seem  to  be  primarily  responsible  for  the  immediate 
chemical  effects  following  stimulation. 

Enzymes  are  simply  colloidal  catalyzers  of  complex 
and  specific  chemical  constitution.  A  part  of  their 
catalytic  acti\dty  presumably  depends  on  their  colloidal 
state;  i.e.,  a  state  of  subdivision  making  surface-condi- 
tions of  preponderant  importance  in  their  chemical 
behavior.  The  general  conditions  of  heterogeneous 
catalysis  thus  apply  to  enzyme  action;  in  addition  there 
are  special  conditions  referable  to  the  specific  stereo- 
chemical configuration  of  the  enzyme  molecule. 

It  is  well  known  that  finely  divided  material  of  various 
kinds  (material  with  large  surface-extent)  is  often  very 


CATALYSIS  AND  BIOCHEMICAL  PROCESSES     223 

active  in  catalyzing  chemical  reactions;  this  is  especially 
true  of  certain  forms  of  carbon  anrl  of  metals  like 
platinum.  The  action  of  platinum  is  especially  well 
known;  it  increases  with  the  state  of  subdivision,  i.e., 
the  extent  of  surface,  hence  colloidal  platinum  is  a  very 
effective  catalyzer.  Other  metals  have  similar  proi)er- 
ties,  although  usually  less  marked. 

Usually  in  such  heterogeneous  catalyses  the  accelera- 
tion of  reaction- velocity  is  regarded  as  a  result  of  in- 
creased concentration  at  the  surfaces.  Faraday  (1839) 
suggested  this  explanation  for  the  action  of  platinum 
in  catalyzing  the  combination  of  hydrogen  and  oxygen. 
In  general,  when  considering  any  special  case  of  hetero- 
geneous catalysis,  three  independent  processes  with 
different  rates  are  taken  into  account:  (i)  the  rate  of 
diffusion  of  the  dissolved  substrate  to  the  active  surface; 
(2)  the  rate  of  adsorption  at  the  surface;  and  (3)  the 
rate  of  chemical  combination.  The  rate  of  reaction  is 
limited  by  the  rate  of  the  slowest  of  these  interdependent 
processes.  In  most  cases  the  reaction- velocity  (F)  is 
regarded  as  determined  by  the  concentration  (C) 
attained  at  the  surface  and  by  the  specific  velocity- 
constant  (K)  of  the  reaction  (i.e.,  V  =  KC),  since  adsorp- 
tion is  rapid  and  also  diffusion  (when  the  distances  are 
small).  The  rate  of  chemical  change  is  increased  (cata- 
lytic effect)  because  the  concentration  of  the  reacting 
molecules  is  increased  in  this  part  of  the  system.^ 

It  is  evident,  however,  that  other  factors  frequently  if 
not  usually  enter  dependent  on  the  special  chemical 
nature   of   the   reacting  compounds.     Many  inorganic 

^  Cf.  Hober's  Physik.  Chemie  der  Zelle,  pp.  702  flf.,  for  an  account  of 
the  general  conditions  of  catalysis  in  heterogeneous  systems. 


2  24   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

catalyses  are  referable  to  the  formation  of  intermediate 
compounds,  and  the  same  is  undoubtedly  true  of  many 
enzyme-reactions.  The  specificity  of  enzymes  and  other 
facts  in  their  behavior  indicate  that  chemical  union 
often  occurs  between  the  enzyme  and  the  substrate 
molecules,  and  that  it  is  the  combination  thus  formed 
which  breaks  down  rapidly,  yielding  the  products  of 
hydrolysis  and  the  free  enzyme,  which  then  repeats  the 
chemical  cycle  of  combination  and  hydrolysis  with  fresh 
molecules  of  substrate. 

Apparently  many  cases  of  heterogeneous  or  contact 
catalysis  are  referable  to  simple  increase  of  concentration 
due  to  adsorption.  But  in  the  case  of  metals  and  other 
conducting  substances  the  possibility  of  an  additional 
factor,  the  formation  of  local  electrical  circuits  between 
different  portions  of  the  active  surface,  is  also  to  be 
considered.  In  either  case  the  essential  condition  is 
some  form  of  surface-action. 

Enzymes  are  colloidal  in  their  condition,  indiffusible, 
precipitable,  readily  adsorbed  by  indifferent  adsorbents, 
and,  according  to  Bayhss,  their  mode  of  action  is  also  a 
surface-action.  The  clearest  proof  of  this  is  that  emulsin, 
lipase,  urease,  and  trypsin  exert  their  action  in  alcohoHc 
media  of  such  a  strength  that  the  enzyme  is  insoluble 
and  can  be  filtered  ofi.^  Bayhss  regards  the  adsorption 
of  the  substrate  on  the  enzyme  phase  as  the  first  step 
in  the  process;  the  chemical  reaction  then  follows.  In 
some  cases  the  adsorption- compound  of  enzyme  with 
substrate  is  separable;  e.g.,  starch- amylase,  fibrin- 
pepsin,  and  trypsin  with  caseinogen.^    A  close  union  or 

^  Cf.  Bayliss,  Principles  of  General  Physiology,  p.  325. 
'  Bayliss,  op.  ciL,  p.  326. 


CATALYSIS  AND  BIOCIIEMIC.\L  PROCESSES      225 

adhesion  of  the  enzyme  to  the  substrate  is  characteristic; 
and  the  influence  of  electrolytes  on  enzyme-processes 
is  probably  in  large  part  to  be  referred  to  their  influence 
on  adsorption.^ 

In  the  simple  adsorption  type  of  catalysis  the  acceler- 
ating effect  depends  on  the  concentration  attained  at  the 
interface.  Close  adhesion  of  the  reacting  compound 
to  the  adsorbent  surface  is  important  since  this  implies 
a  high  concentration  at  the  surface.  Hence  a  corre- 
spondence between  the  molecular  configuration  of  the 
adsorbing  surface  and  of  the  adsorbed  compound  is 
favorable  to  adsorption  as  well  as  to  chemical  combina- 
tion. The  importance  of  such  conditions  is  seen  in  the 
growth  of  crystals,  in  which,  according  to  ]\Iarc,  the 
dissolved  molecules  are  abstracted  from  the  mother- 
liquid  and  deposited  on  the  surface  of  the  crystal  by  a 
process  identical  with  adsorption.^  Slow  growth  is 
favorable  to  the  formation  of  large  crystals,  because 
time  is  then  allowed  for  the  regular  orientation  of  the 
surface-molecules  thus  deposited.  Organic  growth 
apparently  also  depends  on  the  apposition  of  newly 
formed  molecules  to  the  similarly  constituted  molecules 
already  laid  down  in  the  soHd  state  as  structure;  and 
this  consideration  may  explain  why,  in  living  organisms, 
where  definiteness  of  form  and  of  structural  characters 
is  essential,  the  rate  of  growth  is  slow.  Probably  no 
essential  distinction  is  to  be  drawn  between  adsorption 
and  chemical  combination;  in  adsorption  the  surface 
molecules  of  the  adsorbent  are  alone  concerned  because 

»  Cf.  Bayliss,  "Adsorption  as  a  Preliminary  to  Chemical  Reaction," 
Proceedings  of  the  Royal  Society,  B,  LXXXIV  (191 1),  81. 

» Marc,  op.  cit. 


226    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

of  the  solidity  of  the  adsorbing  phase  and  the  remoteness 
of  the  internal  molecules  from  the  sphere  of  reaction. 

SPECIAL  FACTORS  IN  THE  CATALYTIC  ACTION  OF 

PROTOPLASM 

Since  surface-relations  are  all-important  in  hetero- 
geneous catalysis,  all  conditions  modifying  the  composi- 
tion, electrical  polarization,  or  other  characters  of  the 
active  surfaces  influence  the  catalytic  activity  of  the 
system.  Hence  surface-active  substances  as  a  class 
have  a  marked  effect  on  such  catalyses,  and  their  influ- 
ence on  the  chemical  activity  of  living  matter  is  un- 
doubtedly in  large  part  referable  to  this  effect.  A  brief 
review  of  the  action  of  these  substances  on  the  catalytic 
and  other  properties  of  heterogeneous  systems  will 
indicate  the  nature  of  the  factors. 

One  of  the  most  complete  recent  studies  of  the  anti- 
catalytic  action  of  surface-active  substances  on  enzyme 
action  is  that  of  Warburg  and  WieseP  on  the  zymase- 
containing  ''press- juice"  of  yeast.  All  substances  of 
the  anaesthetic  class  retard  the  alcohohc  fermentation 
caused  by  this  enzyme,  although  the  non-Hving  enzyme 
requires  higher  concentrations  than  the  living  cell  for 
the  same  proportional  degree  of  retardation.  In  homolo- 
gous series  the  concentration  necessary  for  a  given  retar- 
dation decreases  in  the  usual  manner  with  increase  of 
molecular  weight.  The  following  orders  of  relative 
action  were  found  for  different  compounds.  Alcohols: 
methyl  <  ethyl  <  propyl  <isobutyl;  urethanes:  ethyl  < 
propyl  <  isobutyl ;  nitriles :  ace  to  <  propio  <  isovalero ; 
ketones :    acetone  <  methyl-propyl  <  methyl-phenyl.      It 

*  Warburg  and  Wiesel,  loc.  cU. 


CATALYSIS  AND  BIOCHEMICAL  PROCESSES     227 

was  also  noted  that  all  of  these  compounds  in  sufTicient 
concentration  caused  precipitation  in  the  press-juice,  and 
that  the  orders  of  relative  precipitating  effectiveness  and 
anticatalytic  action  were  the  same;  this  order  is  also 
that  of  relative  narcotic  action.  This  parallelism 
between  precipitating  action  and  narcotic  action  recalls 
Claud  Bernard's  hypothesis  that  a  partial  coagulation 
of  protoplasmic  constituents  is  the  essential  condition 
of  narcosis.^  With  the  Uving  cell,  however,  much  lower 
concentrations  are  required  to  stop  fermentation  than 
with  the  enzyme  solution,  so  that  the  parallel  between 
the  inactivation  of  the  structureless  enzyme  solution  and 
the  inhibition  of  fermentation  in  the  living  cell  is  not 
complete.  This  difference  may  indicate  the  importance 
of  the  vital  organization  as  such,  or  it  may  depend  on  the 
presence  of  special  compounds  (Upoids)  in  the  li\ing  cell. 
Warburg  and  Wiesel  found,  however,  that  dried  yeast 
cells  (extracted  with  ether  and  acetone)  exhibited  a 
well-marked  fermentative  action,  wliich  was  arrested 
by  narcotic  compounds  in  somewhat  high  concentrations. 
Meyerhof  found  a  closely  similar  anticatalytic  action 
of  the  same  compounds  in  solutions  of  yeast  invertasc;' 
and  in  this  case  also  the  effect  was  associated  with  a 
precipitating  action;  similar  observations  on  oxidase- 
containing  tissue-extracts  have  been  made  by  Hattclli 
and  Stern.^  Vernon'*  also  observed  a  general  inhibitory 
action  of  narcotics  on  tissue-oxidases;    the  effect  was 

^Claude  Bernard,  Leqons  sur  les  AncsUUsiqucs  ct  sur  VAsphyxie, 
Paris  (1875),  P-  154. 

^  Meyerhof,  Arch.  ges.  Physiol,  CLVII  (igu),  251- 

3  Battelli  and  Stem,  Biochcm.  Zeilschrift,  LII  (1913),  226. 

4  Vernon,  Journal  of  Physiology,  XLV  (191 2),  197. 


2  28    PROTOPLAS^nC  ACTION  AND  NERVOUS  ACTION 

imperfectly  reversible  and  may  be  regarded  as  destructive 
rather  than  simply  anti-catalytic.  Narcotics  also  check 
heterogeneous  catalysis  in  purely  inorganic  systems; 
e.g.,  the  oxidation  of  oxahc  acid  by  charcoal  (Warburg)^ 
and  the  decomposition  of  H2O2  by  colloidal  platinum 
(Meyerhof),^  and  the  same  order  of  relative  action  is 
again  seen. 

The  foregoing  association  of  a  precipitating  action 
with  an  anticatalytic  action  indicates  an  alteration  of 
surface-conditions,  but  precipitation  as  such  is  not  a 
necessary  accompaniment  of  this  action.  Many  organic 
compounds  (alcohols)  precipitate  solutions  of  proteins 
and  other  colloidal  compounds,  but  usually  the  con- 
centrations required  for  precipitation  far  exceed  the 
anticatalytic  concentrations. 

Other  effects,  also  dependent  on  surface-action, 
have  an  intimate  bearing  on  the  present  problem.  Of 
special  interest  is  the  action  of  narcotic  compounds  on 
suspensions  of  lecithin.  Changes  in  the  viscosity,  gel- 
forming  properties,  and  precipitabihty  of  lecithin  emul- 
sions are  characteristic.  Many  Hpoid-solvents  (alcohols, 
etc.)  increase  the  viscosity  of  these  emulsions  to  a  greater 
degree  than  can  be  accounted  for  by  the  increase  in  the 
viscosity  of  the  aqueous  phase. ^  In  somewhat  concen- 
trated emulsions  (10-12  per  cent)  the  addition  of  ether 
even  causes  gelation,  so  that  the  test  tube  can  be  inverted 
without  spilling;  this  effect  is  also  caused  by  alcohols 
(n-propyl  up  to  capryl),  esters  (ethyl  formate,  acetate, 

^  Warburg,  Arch.  ges.  Physiol.,  CLV  (1914),  547- 

*  Meyerhof,  Arch.  ges.  Physiol.,  CLVII  (1914),  280. 

3  Handowsky  and  Wagner,  Biochem.  Zeitschrift,  XXXI  (1911),  32; 
A.  Thomas,  Journal  oj  Biological  Chemistry,  XXIII  (1915),  259. 


CATALYSIS  AND  BIOCHEMICAL  PROCESSES     229 

propionate,  and  nitrate),  ethyl  ether,  KtCl,  i:tHr, 
chloretone,  paraldehyde,,  CCI4,  hydrocarbons  like  benzol, 
toluol,  and  xylol,  but  not  by  urethanes  and  lower 
alcohols.^  In  a  lecithin-containing  system  such  as 
protoplasm  this  influence  might  act  anticaUilytically 
by  slowing  diffusion- velocities ;  any  chemical  process 
whose  rate  depended  on  the  rate  of  diffusion  would  thus 
be  retarded.  Increased  hindrance  to  the  movement  of 
ions  would  be  shown  in  decreased  electrical  conductivity. 
Loewe^  has  in  fact  found  that  artificial  membranes 
impregnated  with  lecithin  exhibit  an  increased  electrical 
resistance  in  the  presence  of  anaesthetics;  in  a  system 
Hke  living  protoplasm  such  an  effect  would  retard 
chemical  reactions  dependent  on  electrochemical  con- 
ditions. The  increase  in  viscosity  is  probably  to  be 
referred  in  part  to  the  formation  of  adsorption-films  at 
the  surface  between  the  lecithin  particles  and  the  water.^ 
It  is  possible  also  that  changes  in  the  relative  volumes 
occupied  by  the  colloidal  particles  and  the  aqueous 
phase  may  play  some  part;  presumably  the  lipoid-soluble 
compound  concentrates  in  the  lecithin  in   accordance 

.  .  .       lipoid-solubility,  . 

with    its    partition-ratio,    — : ,  ,  ...^       and    in    so 

^  '    water- solubihty 

doing  enlarges  the  particles;    this  may  explain  why  the 

higher  alcohols  are  more  effective  in  causing  gelation  than 

the    lower    alcohols,    which    are    highly    water-soluble. 

As   the   emulsion   particles   enlarge,    their   freedom   of 

movement  becomes  less,   contacts  are  more  frequent, 

and  coherence  to  a  gel  is  favored. 

^  Cf.  my  review,  The  Theory  of  Anesthesia,  op.  cit.,  p.  362. 
*  Loewe,  loc.  cit.  ^  Cf .  Ibid. 


230    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

It  should  be  noted  that  in  the  case  of  some  other 
colloidal  organic  compounds  the  formation  of  gels  may 
be  prevented  instead  of  promoted  by  the  addition 
of  surface-active  substances;  this  effect  was  observed 
by  Schryver^  in  the  gelation  of  Na-cholate  in  the  presence 
of  various  surface-active  organic  compounds.  He  found 
a  retardation  in  the  rate  of  gelation,  the  effect  running 
in  general  parallel  with  capillary  activity  and  narcotic 
action.  This  phenomenon  is  analogous  to  protective 
action  in  colloidal  precipitation. 

The  protection  of  suspensions  of  lecithin  against 
precipitation  by  electrolytes  is  also  an  effect  character- 
istic of  many  surface-active  compounds.  Hober  and 
Gordon^  found  that  suspensions  containing  ether,  chloro- 
form, chloral,  or  amyl  alcohol  were  less  readily  precipi- 
tated by  alkali-earth  cations  (Ca,  Ba)  than  the  control 
suspensions;  i.e.,  were  stabilized;  and  they  character- 
ized this  action  as  ''narcotization  of  the  plasma  mem- 
brane colloid  lecithin."  Koch  and  MacLean^  found 
that  the  stabilizing  effect  was  not  uniform  with  different 
anaesthetics;  some  compounds  so  act,  but  others  are 
indifferent,  while  stiU  others  further  precipitation, 
especially  the  lower  alcohols  and  paraldehyde,  which  are 
highly  water-soluble.  My  own  observations  on  the 
precipitation  of  lecithin  by  CaCla  and  HCl  confirm  this 
result,  but  they  show  that  at  appropriate  concentrations 
the  great  majority  of  anaesthetics  have  a  stabilizing 
effect.     The    compounds    examined    included    alcohols 

^  Schryver,  Proceedings  of  the  Royal  Society^  By  LXXXVII  (1914), 
366. 

=  Hober  and  Gordon,  Hofmeisters  Beitr.,  V  (1904),  432. 

3  Koch  and  McLean,  Journal  of  Pharmacology  and  Experimental 
Therapeutics,  II  (19 10),  249. 


CATALYSIS  AND  BIOCHE.AIICAL  PROCESSES     231 

from  n-propyl  up,  esters,  urethanes,  hydrocarbons, 
chloroform,  nitromethane,  ethyl  ether,  chloretone,  phenyl 
urea,  and  others.^ 

In  general  these  effects  in  lecithin  suspensions  are 
referable  to  several  factors,  of  which  the  chief  probably 
are  solution  of  the  compound  in  the  colloidal  particles, 
formation  of  adsorption-films  which  change  the  electrical 
polarization  or  other  physical  constants  of  the  particles, 
and  increase  of  viscosity.  The  total  effect  in  most  cases 
is  increase  in  the  physical  stabihty  exhibited  by  the 
system  in  the  presence  of  conditions  tending  to  alter 
the  state  of  aggregation. 

The  protective  influence  exerted  by  proteins  and  other 
surface-active  colloids  in  the  precipitation  of  metallic 
hydrosols  by  electrolytes  is  apparently  a  closely  related 
phenomenon.  Its  conditions  have  been  studied  care- 
fully by  Zsigmondy,"*  who  finds  wide  variations  in  the 
effectiveness  of  different  compounds;  e.g.,  gelatine  is 
highly  effective  as  compared  with  peptone.  He  assigns 
to  each  protective  colloid  a  characteristic  ''gold  number" : 
this  number  defines  the  quantity  of  the  colloid  required 
to  prevent  the  precipitation  of  a  standard  gold  suspension 
by  a  definite  concentration  of  NaCl.  In  tliis  case  the 
protective  effect  undoubtedly  depends  on  the  fonnation 
of  adsorption-films,  which  prevent  coalescence  or  flocking 
of  particles.  Adsorption-films  of  soap,  protein,  or 
similar  substances  play  an  analogous  part  in  the  forma- 
tion of  emulsions,  as  already  pointed  out,  the  susi)cnded 
droplets  being  thus  prevented  from  fusing.  In  a  similar 
manner  these  substances  prevent  sedimentation  in  linely 

^  Cf.  my  The  Theory  of  Anesthesia,  p.  361. 
'  Zsigmondy,  Colloids  and  Ullramicroscopy. 


232    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

divided  suspensions  of  water-insoluble  materials  (chalk, 
Ca-phosphate,  etc.). 

In  his  textbook^  Hober  has  described  various  other 
instances  of  protective  action  and  has  discussed  briefly 
the  general  biological  significance  of  this  phenomenon. 
In  Hving  organisms,  where  water-insoluble  materials 
constitute  an  indispensable  element  in  the  formation  of  all 
permanent  structure,  protective  action  is  of  great  impor- 
tance. Many  otherwise  insoluble  materials  are  thus 
kept  in  a  permanent  state  of  fine  dispersion  or  pseudo- 
solution.  It  is  well  known  that  uric  acid  and  cholesterol 
are  present  in  serum  in  concentrations  far  higher  than 
correspond  to  their  solubiKty  in  water;  presumably 
they  are  held  in  suspension  as  ultra-microscopic  particles 
by  the  protective  action  of  the  serum  proteins.  Pauli 
and  Samec^  have  shown  that  gelatine,  serum  albumin, 
and  other  proteins  may  keep  large  quantities  of  insoluble 
calcium  salts  (sulphate,  phosphate,  carbonate)  in  appar- 
ent solution.  The  silver  salts  in  photographic  plates 
and  the  Ca-phosphate  in  milk  are  other  instances  of 
insoluble  materials  kept  in  fine  dispersion  by  protective 
colloids.  The  suggestion  has  been  made  that  the  forma- 
tion of  pathological  concretions  in  higher  animals 
(gallstones,  uric  acid  deposits)  is  an  expression  of  defi- 
ciency in  protective  colloids.  It  is  probable  that  in  the 
formation  of  normal  structures,  such  as  bone,  by  sepa- 
ration of  insoluble  salts  as  a  finely  divided  and  struc- 
turally regular  deposit,  the  protective  action  of  the  proto- 
plasmic colloids  is  a  necessary  factor;  presumably  in 
the  absence  of  this  factor  the  particles  would  be  flocked 

'  Page  344. 

2  Biochem.  Z.,  XVII  (1909),  235. 


CATALYSIS  AND  BIOCHEMICAL  PROCESSES     233 

by  the  salts  present  and  the  uniform  and  gradual  building 
up  of  regular  structure  would  be  impossible. 

All  of  the  above-described  effects  depend  on  the 
formation  of  interfacial  films  which  alter  the  i)hysical 
properties  of  the  surfaces.  Apparently  also  the  chemical 
or  adsorptive  and  hence  catalytic  properties  of  the 
surfaces  are  secondarily  altered  by  the  deposition  of 
such  foreign  materials;  and  the  foregoing  e\idence  indi- 
cates that  the  anticatalytic  action  of  surface-active 
compounds  depends  on  a  surface-concentration  of  this 
kind. 

Anticatalytic  action  is,  however,  also  well  known  in 
homogeneous  solutions  and  even  in  gases,  so  that  this 
form  of  explanation  does  not  always  apply.  Numerous 
instances  of  anticatalysis  in  homogeneous  solutions  are 
cited  by  Traube  in  his  Theorie  der  Narkose;^  Bigelow's 
observations^  on  the  oxidation  of  NajS03  by  oxygen 
furnish  many  striking  illustrations;  he  found  that  this 
reaction  was  depressed  by  a  large  number  of  organic 
substances;  for  example,  a  trace  of  mannite  (about 
.0014  per  cent)  decreased  the  reaction  velocity  by  50 
per  cent;  benzyl  alcohol  and  aldehyde,  isobutyl  alcoh(-)l 
and  ethyl  alcohol  were  even  more  effective  in  checking 
the  reaction.  It  is  interesting  to  note  that  the  alcohols 
showed  increasing  effectiveness  with  increasing  molecular 
weight,  and  that  the  effect  decreased  with  the  number  of 
hydroxyls  in  the  compound  (e.g.,  monohydroxylic  alco- 
hols >  dihydroxyhc  >  trihydroxylic,  etc).  Aromatic 
compounds  were  more  effective  than  chain  compounds.-* 

^  Arch.  ges.  Physiol,  CLIII  (1913),  279. 

^Bigelow,  Z.  physik.  Chcm.,  XXVI  (189S),  423,  and  XXVII,  5S5. 
3  Many  other  similar  cases  are  cited  in  Traubc's  paper  (the  work  of 
Veley,  Titoff,  Young,  and  others). 


234    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

Anticatalysis  in  homogeneous  solution  has  the  appear- 
ance of  being  a  different  phenomenon  from  the  forms  of 
anticatalysis  considered  above,  and  its  conditions  are 
obscure.  Possibly  the  nearest  analogies  are  with  photo- 
catalysis;  e.g.,  a  catalytic  substance  may  play  a  role 
analogous  to  that  of  a  photochemical  sensitizer;  it  is 
clear  that  interference  with  the  action  of  the  latter  would 
arrest  the  photocatalytic  action.  Just  as  the  chemical 
effect  of  Hght  is  influenced  by  the  presence  of  substances 
with  special  light-absorptive  properties,  as  in  sensitized 
photographic  plates,  so  also  catalysis  by  chemical  com- 
pounds may  be  influenced  by  other  compounds  having 
special  chemical  relations  with  the  catalyzer.  Such 
considerations  are  perhaps  vague,  but  since  many  of 
the  conditions  controlHng  reaction-velocities  are  imper- 
fectly understood,  it  seems  best  not  to  attempt  further 
definiteness  at  present. 


CHAPTER  XI 

ELECTRICAL  AND  OTHER  FACTORS  IN  THE 
CATALYTIC  ACTION  OF  PROTOPLASM 

Of  the  conditions,  other  than  temperature  and  tlie 
presence  of  catalyzers,  influencing  reaction-velocities, 
Hght  and  other  forms  of  radiation  and  electricity  are 
the  most  important.  Apparently  all  chemical  reactions 
are  influenced  by  radiation  of  appropriate  wave-length, 
and  the  acceleration  caused  under  these  conditions  is 
called  ''photocatalysis."  It  differs,  however,  from  the 
chemical  forms  of  catalysis  in  that  energy  is  added  to 
the  reacting  system  from  without;  in  this  respect  the 
conditions  may  be  compared  to  those  present  when  an 
electric  current  is  passed  into  a  solution  from  an  electrode ; 
at  the  surface  of  transition  between  solution  and  electrode 
chemical  reactions  are  induced  (electrolysis),  the  effect 
depending  directly  on  the  quantity  of  electricity  (i.e., 
number  of  electrons)  transferred  between  the  molecules 
of  the  electrode  and  those  of  the  solution.  Similarly 
the  chemical  effect  of  hght  is  referred  to  faciHtation  of  the 
transfer  of  electrons  between  molecules.  In  virtue  of 
its  physical  character  as  electromagnetic  oscillation, 
light  alters  the  range  of  movement  of  the  electrons;  and 
when  the  periodicities  of  electron  motion  and  ether- 
vibration  correspond,  this  range  may  be  increased  to  a 
degree  sufficient  to  enable  adjacent  molecules  to  interact. 
The  electrons  affected  are  apparently  the  valence  or 
combination  electrons  of  the  molecules  concerned. 
The  chemical  action  of  light  is  thus  ultimately  to  bo 

235 


236    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

related  to  its  general  influence  on  electrons,  an  influence 
shown  in  the  photoelectric  effect. 

The  phenomena  of  induced  reactions,  which  are 
almost  certainly  of  great  importance  in  cell-metaboHsm, 
are  probably  also  to  be  affiliated  in  a  general  way  with 
photocatalysis  and  electrolysis  (which  may  perhaps 
be  called  ^'electrocatalysis");  but  it  is  impossible  here 
to  do  more  than  direct  attention  to  these  possibiH- 
ties,  the  investigation  of  which  is  the  subject  of 
physical  chemistry  rather  than  of  biology.  It  is 
sufficiently  evident  that  all  conditions  influencing  chemi- 
cal reaction-velocities  are  of  fundamental  biological 
interest. 

In  considering  the  case  of  heterogeneous  catalysis 
(or  chemical  contact  effects)  and  the  influence  of  anti- 
catalyzers,  the  effect  of  the  latter  on  contact-potentials 
should  be  noted.  These  potentials  are  affected  by  many 
organic  substances,  especially  surface-active  compounds;^ 
the  strength  of  the  current  in  a  battery  and  the  rate  of 
the  associated  chemical  effects  may  thus  be  decreased. 
For  example,  in  the  formation  of  precipitation-structures 
from  zinc  and  Fe  under  the  influence  of  local  circuits, 
the  presence  of  alcohols,  esters,  and  other  surface-active 
compounds  of  the  anaesthetic  groups  has  a  well-marked 
retarding  influence.^  The  concentrations  required  for 
pronounced  retardation  are  similar  to  those  effective  in 
the  above-described  forms  of  anticatalytic  action,  and 
the  effect  may  be  described  as  anticatalytic,  although 
its  conditions  are  probably  complex,  the  influence  on 

'  Cf.  the  papers  of  Gouy,  Abl,  Grumbach,  Loeb  and  Beutner  cited 
below. 

*  Unpublished  observations  of  my  own  in  Clark  University. 


ELECTRICAL  AND  OTHER  FACTORS     237 

viscosity  and  on  adsorption  entering  in  addition  to  that 
on  contact-potentials. 

In  a  recent  review  of  the  facts  and  theories  of  contact- 
catalysis  Bancroft^  cites  various  instances  where  electrol- 
ysis and  electrode-potentials  are  altered  by  foreign 
substances.  Thus  the  P.D.  at  which  O,  is  freed  at  a 
platinum  surface  is  found  to  be  influenced  by  the  electro- 
lytes present.  With  platinum  electrodes  oxidations 
occur  more  readily  at  platinized  than  at  smooth  surfaces, 
apparently  because  of  the  '^ catalytic"  action  of  the 
finely  divided  platinum.  The  presence  of  cyanide  and 
other  compounds  reduces  the  rate  of  oxidation  occurring 
at  an  electrode  under  a  given  P.D.;  for  example,  a 
neutral  solution  of  Na2S203  is  oxidized  to  tetrathionate 
at  a  platinized  anode  with  a  P.D.  of  0.44  volts  and  a 
current-density  of  3X10"'*  amperes  per  square  centime- 
ter. If  a  trace  of  Hg(CN)2  is  added,  the  anode  P.D.  for 
the  same  current  rises  to  0.48  volts.  Various  salts  have 
marked  influence  on  the  electrochemical  processes  at 
smooth  anodes.^  Gouy^  made  an  extensive  study  of  the 
eflfects  of  various  compounds  on  the  surface-tension 
maxima  in  the  capiflary  electrometer.  Usually  this 
maximum  corresponds  to  a  minimal  P.D.  between  the 
Hg  and  the  U,  SO4;  but  the  P.D.  and  the  surface-tension 
are  both  changed  by  the  substance  added,  so  that  the 
position  of  the  maximum  is  shifted,  and  this  influence 
was  found  to  be  greatest  with  highly  surface-active 
substances.     Similar  observ-ations  were  made   by  Abl 

"  Bancroft,  Journal  of  Physical  Chemistry,  XXI  (191 7),  734- 

'Cf.  Foerster,  Elektrochemie  wassrigcr  Losungcn  (19 15)  for  further 

details. 

3  Gouy,  Ann.  de  Chim.  el  de  Phys.,  XXIX  (1903),  US',  VIII  (1906), 

291,  and  IX,  75. 


238    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

on  the  electromotive  force  of  cadmium-amalgam  cells/ 
In  the  case  of  contact-potentials  between  water  and  other 
dielectrics,  Grumbach^  found  in  general  that  organic 
compounds  which  lower  the  surface-tension  of  water 
decrease  these  potentials.  With  CH3OH,  C2  HgOH,  and 
C4H9OH  the  effect  increases  in  the  order  of  increasing 
molecular  weight;  the  curves  relating  potential  change 
and  concentration  resemble  the  corresponding  curves  of 
surface-tension  and  adsorption.  The  observations  of 
Loeb  and  Beutner^  on  the  contact-potentials  between 
organic  membranes  (apple  skin)  and  electrolyte  solutions 
containing  alcohols  also  show  a  decrease  of  P.D.  with 
the  addition  of  alcohol.  With  the  first  three  alcohols 
the  effect  increased  was  in  the  order  of  Ci<C2<C3 
(p.  302).  Similar  results  were  obtained  with  solutions  of 
lecithin  in  guaiacol.  The  concentrations  required  to 
produce  a  decided  influence  on  the  potentials  were, 
however,  much  higher  than  the  physiologically  effective 
or  narcotizing  concentrations. 

Traube  nevertheless  regards  the  influence  of  surface- 
active  substances  on  the  contact-potentials  between  the 
living  cell  and  the  medium  as  an  important  factor  in  the 
physiological  effect,  and  Macallum  has  expressed  a 
similar  view."*  It  is  doubtful,  however,  if  this  can  be 
generally  true,  since  the  bioelectric  potentials  are  not 
necessarily  decreased  in  anaesthesia.  For  example,  in 
pure  sugar  solution,  which  produces  in  muscle  effects 

*  Cf.  Traube,  "Theorie  der  Narkose,"  Arch.  ges.  Physiol.,  CLIII 
(1913),  276;  cf.  p.  303. 

2  Ann.  de  Chim.  et  de  Phys.  (191 1). 

3  Biochem.  Zeitschrift,  LI  (1913),  300. 

4  A.  B.  Macallum,  Surface  Tension  and  Vital  Phenomena,  University 
of  Toronto  Studies  (1912),  No.  8,  pp.  68  £f. 


ELECTRICAL  AND  OTHER  FACTORS  239 

similar  to  anaesthesia,  the  bioelectric  P.D.  is  incrcasecl.' 
The  local  negativity  produced  by  anaesthetics  under 
certain  conditions,  as  in  Allcock's  experiments,^  is 
probably  to  be  referred  to  the  permeability-increasing 
effect  of  the  compounds  in  higher  concentrations. 

The  connection  between  adsorption  and  contact 
catalytic  action  has  been  usually  regarded  as  a  special 
case  of  the  mass-action  law.  Since  any  increase  in  the 
concentration  of  a  reacting  substance  involves  a  propor- 
tional increase  in  reaction-velocity,  and  since  the  concen- 
tration of  many  dissolved  substances  is  increased  in  the 
layer  of  solution  adjoining  an  interface,  it  follows  that 
in  any  such  case  there  must  be  increased  reaction- 
velocity  in  that  region.  Hence  if  the  adsorbing 
surface  is  sufficient  in  area,  as  with  fine  subdivision,  a 
large  proportion  of  the  reacting  material  may  be  present 
in  the  surface  layer  at  any  time,  and  a  considerable 
increase  in  reaction- velocity  may  result.  Direct  parallels 
between  adsorption  and  catalysis  have  in  fact  been 
observed  in  certain  cases.^ 

It  is,  however,  questionable  if  this  influence  is  in 
itself  sufficient  to  account  for  the  effects  observed;  in 
many  cases  the  surface  appears  to  exercise  some  specific 
chemical  influence;  and  certain  contact  catalyzers, 
especially  platinum,  have  an  accelerative  action  which  is 
far  greater  than  can  be  accounted  for  on  the  ground  of 
their  adsorptive  capacity  alone.'* 

^Cf.  Briinings,  Arch.  ges.  Physiol,  XCVIII  (1903),  241.  M:ic- 
donald's  work  also  shows  an  increase  of  the  demarcation  potential  with 
decrease  in  the  external  electrolyte  content.     Cf.  p.  304. 

2  Allcock,  Proceedings  of  the  Royal  Society,  B,  LXXVII  (1906),  p.  267. 

3  Cf.  Hober's  Physik.  Chcmic  d.  Zclle  (1914),  P-  705- 

4  Cf.  Bancroft's  Applied  Colloid  Chemistry,  p.  40. 


240    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

From  the  physiological  point  of  view  the  chief  case 
of  specific  acceleration  by  a  finely  dispersed  or  colloidal 
catalyzer  is  enzyme  action.  There  seems  to  be  no  doubt 
that  in  many  cases  the  enzyme  acts  through  the  forma- 
tion of  intermediate  compounds,  which  break  down  at 
high  velocity  yielding  the  decomposition  products  and  the 
original  enzyme,  the  latter  then  recombining  with  the 
substrate  molecules  to  repeat  the  cycle.  The  formation 
of  the  enzyme-substrate  combination  presupposes  inti- 
mate contact  between  the  molecules  of  enzyme  and 
substrate;  hence  a  correspondence  in  size  and  pattern 
between  the  intercombining  molecules  (or  parts  of 
molecules;  e.g.,  zymophore  groups)  is  required,  of  the 
kind  indicated  by  the  ''lock  and  key"  comparison  of 
Emil  Fischer.  That  relations  of  this  kind  play  a  part 
in  adsorption  is  indicated  by  Marc's  observation  that  a 
crystalline  adsorbent  like  BaS04  exhibits  preferential 
adsorption  for  compounds  crystallizing  in  the  same 
system.^  Apparently  this  is  a  simple  instance  of  specific 
adsorption.  Close  contact  of  this  kind  gives  the  occasion 
for  chemical  transformations  (hydrolysis,  etc.)  which 
otherwise  would  not  occur,  or  at  much  lower  velocity. 
According  to  Bayliss^  a  simple  reversible  adsorption 
often  precedes  a  more  intimate  "chemical"  union 
between  adsorbent  and  adsorbed  substance.  In  specific 
catalyses,  like  those  induced  by  enzymes,  factors  of 
a  similar  kind  probably  enter;  the  union  is  specific 
because  of  the  similarity  of  molecular  configuration 
between  enzyme  and  substrate,  and  the  chemical  effect 
follows  because   the   enzyme-substrate   combination  is 

'  Cf .  Marc,  loc.  cit. 

^  Bayliss,  Proceedings  of  the  Royal  Society,  B,  LXXXIV  (191 1),  p.  269. 


ELECTRICAL  AND  OTHER  FACTORS     241 

unstable  and  breaks  down  in  the  manner  already 
indicated. 

Catalytic  effects  due  to  simple  increase  in  concentra- 
tion are  accordingly  to  be  distinguished  from  those  which 
depend  on  the  appearance  of  special  relations  of  some 
kind  between  the  molecules  of  the  substrate  and  of  the 
catalyzer.  In  the  latter  case  the  formation  of  combina- 
tions differing  from  the  substrate  in  reactivity,  e.g., 
velocity  of  hydrolysis  or  oxidation,  becomes  possible; 
and  when  these  temporary  combinations  break  down, 
setting  free  the  catalyzer  and  enabling  the  latter  to 
repeat  the  combination,  the  total  effect  is  the  same  as  if 
chemical  change  in  the  substrate  alone  were  accelerated. 
The  general  theory  of  intermediate  compound  formation 
would  thus  apply  to  any  specific  adsorption-catalysis. 
The  adsorbent  would  correspond  to  the  enzyme,  and  the 
theory  of  such  catalysis  need  not  differ  in  principle 
from  that  of  catalysis  in  homogeneous  solutions;  e.g., 
H-ion  catalysis.  At  present,  however,  there  appears  to 
be  no  completely  satisfactory  theory  of  this  type  of 
catalysis. 

With  regard  to  other  conditions  which  may  enter  in 
cases  of  heterogeneous  catalysis,  it  has  been  suggested 
that  the  increased  reaction- velocities  shown  by  many 
substances  (sugars,  etc.)  in  protoplasm  are  phenomena 
of  the  same  kind  as  the  differences  of  velocity  shown  by  a 
given  reaction  in  different  solvents,  as  obser\-ed  by 
Menschutkin  and  others.'  Bredig  comjxires  a  ])article 
of  a  solid  catalytic  agent  with  a  drop  of  hquid,  and  regards 
the  formation  of  an  adsorption-tilm  as  equivalent   to 

I  Menschutkin,  Z.  physik.  Chcm.,  XI  (1SS7),  611;  von  Ilalban, 
ibid.y  LXXXII  (1913),  325-    Cf.  Hciber,  op.  cit.,  p.  704- 


242    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

solution;^  in  this  case  different  reaction-products  might 
be  obtained  from  the  same  reaction-mixture  under  the 
influence  of  different  catalytic  agents,  differences  of 
adsorption  having  the  same  effect  as  differences  of 
solubiHty.  Selective  adsorption  and  selective  catalysis 
would  thus  be  referred  to  the  same  conditions,  and  both 
referred  ultimately  to  the  same  conditions  as  selective 
solubility.  At  present  there  is  an  increasing  tendency 
to  regard  both  solution  and  adsorption  as  special  cases 
of  chemical  combination.  But  although  protoplasm 
contains  solvents  in  which  it  is  conceivable  that  certain 
reactions  may  proceed  with  increased  velocities,  it  does 
not  seem  probable  that  such  considerations  can  explain 
the  high  velocities  of  the  biologically  more  important 
reactions,  such  as  the  oxidation  of  sugar.  Many  facts, 
especially  the  phenomena  of  irritability,  show  that  the 
conditions  determining  the  increase  of  reaction- velocities 
in  protoplasm  are  of  a  special  kind  and  that  the  factor 
of  organized  structure  is  all-important.  It  is  not 
simply  a  case  of  transferring  a  substance  from  a  solvent 
in  which  its  reaction-velocity  is  low  to  one  in  which  it 
is  high. 

It  has  been  pointed  out  by  various  authors  that  when 
adsorption  is  highly  selective,  displacements  of  equi- 
Hbrium  may  occur;  thus  an  adsorbent  may  change  the 
H-ion  concentration  of  a  solution.  Such  effects  may 
be  attributed  to  the  selective  adsorption  of  ions  (Freund- 
lich)  ;^  but,  as  we  have  seen,  the  distinction  between  the 
adsorption  of  a  substance  and  its  chemical  combination 
with  the  surface  molecules  of  the  adsorbent  cannot  be 

^  Cf.  Bredig,  Ergebnisse  der  Physiol.,  I  (1902),  211. 
2  Cf .  Freundlich,  Kapillarchemie, 


ELECTRICAL  .\ND  OTHER  FACTORS     243 

sharply  drawn.  If,  in  fact,  the  two  processes  are 
indistinguishable,  the  case  becomes  essentially  one  of 
alteration  of  equiUbrium  following  the  introduction  of  an 
additional  reagent  into  a  reaction-mixture.  Bancroft 
cites  instances  where  the  same  compound  undergoes 
different  reactions  under  other^vise  similar  conditions 
according  to  the  nature  of  the  contact-agent  ]:)resent;' 
thus  with  colloidal  nickel  as  catalyzer,  alcohol  forms 
acetaldehyde  and  hydrogen,  while  with  colloidal  silica 
or  alumina  it  forms  ethylene  and  water;  and  he  refers 
this  difference  in  the  catalytic  action  to  the  dilTerences 
in  the  selective  adsorptive  action  of  the  two  substances, 
nickel  adsorbing  hydrogen  and  alumina  water.  The  rate 
and  character  of  the  reaction  undergone  by  a  given 
reaction-mixture  may  thus  vary  with  the  character  of 
the  catalyzer,  according  to  the  latter's  special  adsorbent 
properties. 

It  has  been  mentioned  that  simple  adsorj^tion  is 
insufficient  to  account  for  the  great  activity  of  certain 
contact  catalyzers.  Taylor^  points  out  that  charcoal 
adsorbs  carbon  monoxide  and  oxygen  but  does  not 
catalyze  the  reaction;  but  in  the  case  of  ethylene  and 
oxygen  it  both  adsorbs  and  catalyzes;  hence  as  catalyzer, 
it  differentiates  between  carbon  monoxide  and  ethylene, 
although  adsorbing  both.  MetalHc  oxides,  on  the 
contrary,  catalyze  the  oxidation  of  carbon  monoxide. 
It  would  appear,  therefore,  that  specific,  i^rcsiimably 
chemical,  relationships  enter  even  in  such  simple  cases. 

» Bancroft,  Journal  of  Physical  Chemistry,  XXI  (i9»7)»  573; 
Applied  Colloid  Chemistry,  pp.  40  fif. 

»Hugh  S.  Taylor,  Trans.  Amcr.  Elcdrochcm.  Soc,  XXX\'I  (1919)1 
150. 


244  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

Facts  like  these  (the  so-called  '^ preferential  catalysis") 
may  be  regarded  as  e\idence  of  conditions  which  in 
their  higher  developments  in  Hving  organisms  appear 
as  the  highly  selective  specificity  of  many  enzymes. 

The  recent  work  of  Langmuir  and  Harkins^  has 
shown  that  molecules  assume  definite  orientations  at  the 
surfaces  at  which  they  are  adsorbed.  This  orientation  is 
undoubtedly  a  factor  in  the  chemical  effect  produced; 
reactive  groups  may  thus  be  brought  into  a  position  in 
which  they  more  readily  come  into  contact  with  other 
molecules  (or  the  reactive  groups  of  other  molecules), 
and  in  this  manner  reaction  is  furthered.  Cases  of 
preferential  catalysis  may  thus  be  explained.  The 
catalytic  effectiveness  of  phase-boundaries  exhibits  itself 
in  many  remarkable  ways.  Taylor  and  Langmuir^ 
cite  Faraday's  observation  that  a  perfect  crystal  of 
sodium  sulphate  does  not  efiioresce  until  its  surface  is 
scratched  or  broken,  when  the  effiorescence  spreads  from 
the  injured  part  over  the  rest  of  the  crystal.  Other 
similar  examples  are  well  known;  apparently  the 
reactivity  of  molecules  is  altered  by  the  adjacent 
molecules  of  reaction-product:  the  use  of  ''catalyst- 
promoters"  in  chemical  processes  illustrates  the  same 
phenomenon.  Enhanced  reactivity  at  interfaces  is  in 
fact  a  very  general  phenomenon;  and  in  Hving  matter, 
with  its  polyphasic  constitution,  the  conditions  are 
exceptionally  favorable  for  this  type  of  influence. 

'  Langmuir,  loc.  cit.;  Harkins,  loc.  cit. 

2  H.  S.  Taylor,  "  Catalysis  and  Catalytic  Agents  in  Chemical  Pro- 
cesses," Jour.  Franklin  Inst.,  CXCIV  (1922),  i;  Langmuir,  "Chemical 
Reactions  at  Surfaces,"  Trans.  Faraday  Soc,  XVII  (192 1),  Part  III 
(September);  reprinted  in  Gen.  Elec.  Rev.,  XXV  (1922),  445. 


ELECTRICAL  AND  OTHER  FAC  TORS  245 

It  is  probably  significant  that  the  substances  which 
effect  the  greatest  variety  of  contact  catalyses,  carbon 
and  the  metals,  especially  platinum,  belong  in  the  class 
of  metallic  conductors.'  In  such  conductors,  according 
to  the  electron  theory,  there  is  ready  transfer  of  electrons 
from  atom  to  atom,  hence  their  electrical  conductivity, 
and  other  properties  correlated  with  this  peculiarity 
(optical,  etc.).  It  might  be  expected  that  such  sub- 
stances would  also  facihtate  the  transfer  of  electrons  to 
or  from  molecules  with  which  they  are  in  contact,  and 
thus  furnish  the  conditions  necessary  for  chemical 
reaction.  In  other  words,  factors  characteristic  of  the 
metallic  state  may  enter  in  contact-catalysis;  for 
example,  the  formation  of  local  electrical  circuits  between 
different  parts  of  the  metaUic  surface,  or  oscillation 
phenomena  of  a  frequency  corresponding  with  that  of 
the  combination-electrons  of  the  interacting  substances 
(resonator  effects).  An  example  of  the  former  ty})e  of 
influence  was  seen  in  the  simple  experiment  described 
above,  in  w^hich  the  contact  of  a  nobler  metal  or  carbon 
accelerates  or  "catalyzes"  the  formation  of  ferricyanide 
filaments  from  zinc.  Combinations  of  two  contact 
catalyzers  seem  often  to  be  more  effective  than  either 
one  alone;  thus  Shenstone  found  that  "platinized 
charcoal"  was  extremely  effective  in  oxidizing  alcohol, 
"converting  spirits  of  wine  into  \inegar  in  a  lew  hours," 
and  other  cases  of  a  similar  kind  are  described  by  Bancroft 
in  a  recent  review.^  Presumably  the  two  comj)onrnls 
differ  in  their  potential-difference  against  the  medium, 

^  Contrast,  e.g.,  the  lack  of  catalytic  power  in  colloidal  silica  (cf. 
Taylor,  Trans.  Amer.  Eleclrochcm.  Soc,  op.  cit.,  p.  150). 

^Journal  of  Physical  Chemistry,  XXI  (1917),  644;  cf.  pp.  607  iT. 


246    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

and  thus  local  circuits  arise  which  have  chemical  effects. 
Rideal  and  Taylor  also  describe  cases  where  metallic 
couples  have  a  greater  catalytic  effect  than  either  metal 
singly.^  The  readiness  with  which  the  metalHc  phase 
conducts  electricity  enables  any  local  inequaHties  in  the 
metal,  or  in  the  nature  or  concentration  of  materials  (e.g., 
salts  and  oxidizable  and  reducible  compounds)  present 
in  the  solution,  to  give  rise  to  electric  currents  between 
different  parts  of  the  surface.  These  local  currents  may 
secondarily  influence  chemical  reactions,  as  in  other  cases 
of  electrolysis  at  metallic  electrodes.  Effects  of  the 
reverse  or  anticatalytic  kind  may  result  when  the  metal- 
lic surface  is  altered  in  such  a  way  as  to  lessen  the  local 
potential-differences  or  increase  the  resistance  of  the  local 
circuits;  strongly  adsorbed  organic  compounds  may 
have  both  of  these  effects,  as  already  pointed  out. 

Electrochemical  oxidations  at  platinum  anodes  are 
subject  to  variations  (partly  mentioned  above)  which 
are  possibly  referable  to  the  existence  of  local  circuits; 
these  exercise  their  own  influence  independently  of  the 
E.M.F.  appHed  from  without,  and  give  rise  to  inter- 
ference and  summation  phenomena  of  various  kinds. 
The  possibiUty  that  the  formation  of  local  circuits  plays 
a  part  in  the  normal  catalytic  activity  of  platinum  and 
other  metals  in  liquid  systems  seems  to  have  been 
insufficiently  considered  by  chemists.  The  essential 
conditions  of  such  catalysis  are  perhaps  best  illustrated 
by  the  decomposition  of  hydrogen  peroxide,  which  is 
effected  by  a  large  number  of  finely  divided  metals  of 
which    platinum    is    especially    active.     The    striking 

^  Rideal  and  Taylor,  Catalysis  in  Theory  and  Practice  (Macmillan, 
1919),  pp.  130,  160. 


ELECTRICAL  AND  OTHER  FACTORS     247 

parallels  between  this  action  and  the  similar  action  of 
organic  fluids  and  cell-extracts  ha\e  Ion*;  been  known. 
The  decomposition  of  H^O^  by  living  tissues  is  now 
regarded  as  due  to  a  special  enzyme,  catalase.  The 
relation  of  this  catalytic  action  of  tissue-extracts  to 
enzyme  action  and  fermentation  was  early  recognized 
by  Schonbein,  who  characterized  the  splitting  of  U,(),  as 
a  model  or  prototype  of  all  fermentative  processes 
(Urbild  alter  Gdhrimgen).'-  A  study  of  the  conditions 
under  which  it  occurs  in  the  presence  of  metals  may  thus 
throw  some  Hght  on  the  general  nature  of  catalytic  elTects 
in  heterogeneous  systems  and  especially  in  li\ing  proto- 
plasm. 

Among  other  metals  mercury  shows  great  activity  in 
decomposing  H2O2.  The  most  striking  feature  of  the 
catalytic  decomposition  of  H2O2  in  contact  with  a  mercury 
surface  is  that  under  certain  conditions  the  process 
exhibits  a  definite  regular  rhythm,  closely  resembling 
physiological  rhythms  Kke  that  of  the  heart  beat  in  its 
frequency,  in  its  dependence  on  temperature  (Q,o  =  about 
2),  and  in  the  influence  exerted  upon  it  by  chemical  and 
electrical  conditions.  This  phenomenon  lias  lately  been 
the  subject  of  much  investigation,  specially  by  Brcdig 
and  his  students,  and  its  detailed  conditions  have  been 
studied  most  closely  by  AntropofT.^  The  chief  result 
of  this  study  has  been  to  show  that  the  catalytic  rhythm 
is  dependent  on  the  alternate  formation  and  dissolution 
of  a  surface-film  of  oxidation-product  (''peroxidatc") 
formed  by  interaction  between  the  mercury  and  the 
peroxide.     Since  evidence  from  various  sides  inch'cates 

»  Schoenbein,  /.  prakl.  Cficm.,  LXXXIX  (1863),  335. 
=»  Antropoflf,  Z.  pliysik.  Chem.,  LXII  (1907),  S^i- 


248    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

that  many  vital  processes  (stimulation,  cell-division) 
are  also  dependent  on  changes  undergone  by  surface- 
films — those  forming  the  plasma  membranes  and  other 
protoplasmic  partitions — this  feature  of  the  H2O2  ca- 
talysis suggests  that  the  foregoing  physiological  parallel 
may  be  more  than  a  superficial  one,  and  that  the  similari- 
ties depend  on  a  fundamental  identity  in  the  conditions 
controlling  the  course  of  the  reactions  in  the  two  systems. 
It  is  necessary  therefore  to  examine  more  closely  into 
the  nature  of  the  conditions  controlHng  the  activity  of 
the  Hg-HaOa  system. 

The  rhythm  is  best  shown  in  10  per  cent  aqueous 
solutions  of  H2O2.  The  film  which  forms  over  the  surface 
of  pure  mercury  in  this  solution  is  gold-brown  in  color, 
and  the  conditions  for  the  rhythmical  reaction  are  best 
when  the  solution  is  shghtly  on  the  alkaline  side  of 
neutrality.  The  evolution  of  oxygen  occurs  during  the 
breaking  down  of  the  film;  when  the  film  covers  the 
entire  surface  of  the  mercury  the  reaction  ceases.  If 
the  solution  is  shghtly  acid,  the  film  is  stabilized  and 
no  evolution  of  gas  occurs;  at  the  appropriate  degree  of 
alkahnity  it  is  alternately  formed  and  broken  down  with 
a  regular  rhythm  of  about  ten  to  fifteen  per  minute 
(at  18°) .  The  film  shows  great  sensitivity  to  the  presence 
of  foreign  substances,  including  salts  and  surface-active 
organic  compounds  (such  as  ether  and  olive  oil);  the 
latter  abolish  the  rhythm.^  It  is  also  highly  susceptible 
,to  changes  in  electrical  polarization.  Many  other 
striking  parallels  with  physiological  rhythms  are 
described  in  the  article  by  Bredig  and  Wilke.^ 

^  Cf.  Bredig  and  Weinmayr,  Z.  physik.  Chem.,  XIJI  (1903),  601. 
'  Biochem.  Zeitschrift,  XI  (1908),  67. 


ELECTRICAL  AND  OTHER  FACTORS     249 

The  fact  indicating  most  clearly  the  essential  nature 
of  the  conditions  governing  the  course  of  the  reaction  is 
that  the  rhythm  of  decomposition  is  associated  with  a 
parallel  rhythm  of  electrical  potential.  I'he  mercury 
in  contact  with  the  H^O^  solution  is  always  found 
cathodal  wdth  reference  to  the  calomel  electrode,  but 
during  the  active  phase,  while  O2  is  being  freed,  it  is  less 
so  than  during  rest;  i.e.,  the  metal  becomes  anodal 
relatively  to  the  resting  condition.  According  to 
Antropoff's  measurements,  the  inactive  mercury  is 
about  0.12  volt  more  cathodal  (i.e.,  nobler)  than  the 
active.  This  difference  resembles  that  between  passive 
and  active  iron  in  nitric  acid  solution,  the  inactive 
mercury  corresponding  to  the  passive  iron.  A  change 
of  surface-tension  accompanies  the  change  of  potential, 
the  rounded  convex  surface  of  the  mercury  becoming 
flatter  (from  decreased  surface-tension)  as  the  film 
forms;  this  behavior  is  in  accordance  with  the  Lippmann- 
Helmholtz  rule  of  electrocapillarity,  according  to  which 
the  surface-tension  decreases  with  increase  of  the 
potential-difference  across  the  surface.  Graphic  registra- 
tion of  the  curve  of  potential  change  shows  that  its 
course  runs  closely  parallel  with  the  curve  of  oxygen 
evolution  as  measured  by  a  manometer. 

Close  observation  shows  that  the  gas  is  evolved  only 
during  those  times  when  part  of  the  mercury  is  film- 
covered  and  part  bare;  further,  that  the  evolution  of  gas 
occurs  chiefly  near  the  boundary  between  the  bright 
and  the  film-covered  surfaces.  Wicn  a  regular  rhythm 
is  established,  the  reaction  during  each  cycle  is  observed 
to  pass  rapidly  over  the  surface  of  the  mercury  in  a 
wavelike  fashion.     At  the  beginning  of  a   cycle,   when 


250   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

the  whole  mercury  surface  is  film-covered  and  inactive 
and  is  flattening  as  a  result  of  the  lowering  of  surface- 
tension,  a  rupture  of  the  film  appears,  usually  at  the 
margin  of  the  drop,  disclosing  the  bright  metalHc  surface 
beneath.  Instantly  an  effervescence  starts  at  the  edges 
of  this  fissure  and  then  sweeps  over  the  whole  surface  of 
the  metal;  a  new  film  is  then  formed  and  the  cycle  is 
repeated.  In  an  inactive  drop,  an  artificial  mechanical 
rupture  will  often  initiate  a  reaction  which  similarly 
spreads  rapidly  over  the  whole  surface. 

Bredig  found  that  a  stationary  film  formed  over  an 
inactive  surface  of  mercury  is  quickly  dissolved  by  render- 
ing the  metal  cathode;^  in  this  process  of  dissolution 
oxygen  is  freed.  The  essential  condition  of  the  transmis- 
sion thus  becomes  clear.  When  a  film-covered  and  a 
bright  area  of  the  mercury  surface  adjoin  each  other, 
e.g.,  after  a  local  rupture  of  the  film,  a  local  electrical 
circuit  is  formed  between  the  two,  the  film-covered 
area  being  the  cathode  of  the  local  circuit.  The  current 
of  this  circuit  has  the  effect  of  dissolving  the  film,  by 
cathodic  reduction,  for  a  certain  distance  (estimated  at 
1-3  millimeters)  from  the  boundary,  oxygen  being  freed 
in  the  process;  and  by  repetition  of  this  effect  at  each 
new  boundary  as  soon  as  it  is  formed  the  effect  spreads 
rapidly  over  the  whole  surface.  The  Hg-HaOa  pulsating 
catalysis  thus  in  reality  represents  an  intermittent 
electrolysis  of  H2O2  under  the  influence  of  the  temporary 
local  circuits  formed  during  the  alteration  or  removal 
of  the  surface-film. 

Rhythmical  chemical  processes  at  the  surfaces  of 
metals    immersed    in    electrolyte    solutions    containing 

^  Cf.  Bredig  and  Wilke,  op.  cit.,  p.  69. 


ELECTRICAL  AND  OTHER  FACTORS     251 

compounds  which  interact  with  the  metal  arc  not 
infrequent;'  e.g.,  when  the  metal  is  undergoing  solution 
in  a  strongly  oxidizing  acid  Hke  HNO3.  Iron  in  particular 
often  illustrates  this  phenomenon  with  great  beauty  and 
regularity;  in  this  case  the  essential  condition  of  the 
rhythm  is  an  alternation  between  active  and  passive 
states,  due,  as  in  the  mercury  catalysis,  to  the  alternate 
formation  and  dissolution  of  a  protective  surface-hlm  of 
oxidation-product.  All  of  these  inorganic  rhythms  are 
highly  susceptible  to  variations  in  external  conditions, 
and  especially  to  electrical  influences. 

The  rhythmical  processes  so  frequent  in  living 
organisms  (rhythms  of  cilia,  muscle,  nerve  cells,  vacuoles, 
and  cell-division)  show  many  close  parallels  with  these 
inorganic  ''surface-reaction"  rhythms.  As  in  metals, 
they  are  associated  with  rhythmical  variations  of  electri- 
cal potential  and  with  rhythms  of  chemical  or  metaboUc 
alteration  and  surface-change  (clearly  demonstrable,  e.g., 
in  cell-division),  and  are  similarly  susceptible  to  changes 
in  the  surrounding  conditions  (temperature,  H-ion 
concentration,  presence  of  salts  and  surface-active 
compounds,  electrical  polarization,  etc.) .  These  parallels 
imply  a  similarity  in  the  essential  determining  conditions 
in  the  living  and  the  non-living  systems.  Since  rhythmi- 
cal catalysis  in  metals  is  dependent  on  the  polyphasic 
character  of  the  system — tliis  being  the  condition  which 
makes  possible  rapid  local  variations  of  potential, 
resulting  from  changes  in  the  composition  and  structure 
of  surface-films — the  hypothesis  that  the  organic  rhythms 
are  similarly  conditioned  naturally  suggests  itself, 
particularly  when   the   film-pervaded   or  emulsion-like 

^  For  earlier  observations  cf.  Bredig  and  Wicnmayr,  loc.  cU. 


252    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

structure  of  living  matter  and  the  various  facts  showing 
the  dependence  of  stimulation  on  membrane  processes 
are  taken  into  consideration.  The  general  susceptibility 
of  living  matter  to  electrical  influence  suggests  that  in 
protoplasm  there  may  be  a  similar  dependence  of  the 
chemical  reactions  upon  processes  of  electrolysis  occurring 
at  the  boundaries  between  the  protoplasmic  phases. 
This  general  interpretation  is  also  consistent  with  the 
readiness  and  rapidity  with  which  chemical  influence  is 
transmitted  from  region  to  region  in  Kving  matter; 
the  many  close  resemblances  between  such  transmissions 
and  the  transmission  of  the  waves  of  electro-chemical 
alteration  over  the  surface  of  mercury  or  passive  iron  will 
be  considered  later  in  detail.  In  these  inorganic  systems 
the  chemical  reactions  are  directly  determined  by  the 
potential-differences  existing  between  different  portions 
of  the  metalHc  surface;  these  potential-differences  arise 
as  the  result  of  local  alterations  of  the  surface-films,  and 
the  local  circuits  thus  arising  effect  the  chemical  change 
by  electrolysis.  Similarly  in  living  matter  the  waves  of 
chemical  and  physiological  alteration  accompanying  the 
transmission  of  stimulation  (i.e.,  excitation-waves,  nerve- 
impulses,  etc.)  are  always  associated  with  waves  of 
electromotor  variation.  Bernstein  first  showed  for 
motor  nerves  (in  1866)  that  the  physiological  effect  and 
the  bioelectric  variation  have  the  same  velocity  of  propa- 
gation;^ and  all  of  the  more  recent  evidence  confirms 
the  view  that  the  electric  variation  is  the  essential 
component  of  the  transmitted  process. 

Recently  I  have  discussed  in  some  detail  the  parallels 
between  the  transmission  of  chemical  effects  in  systems 

Cf.  Bernstein's  Elektrohiologie,  chap,  iii,  for  references. 


ELECTRICAL  AND  OTHER  FACTORS     253 

consisting  of  metals  immersed  in  electrolyte  solutions 
and  the  transmission  of  physiological  influence  in  H\ing 
protoplasm.^  In  all  such  phenomena  in  metals  the 
essential  condition  is  the  presence  of  a  thin  film  of  electro- 
chemically  alterable  material  formed  or  deposited  at 
the  interface  between  the  metal  and  the  electrolyte 
solution.  Local  circuits  between  adjoining  regions  of  the 
film-covered  surface,  differing  in  composition  or  physical 
condition  in  such  a  manner  as  to  give  rise  to  an  E3LF. 
sufficient  for  electrolysis,  are  in  all  cases  the  essential 
factor.  By  the  action  of  these  local  currents  the  film 
is  locally  altered  or  removed   or  rendered  permeable 


»iAI,,vU.-,W-<.'tA'>'.'.Vi:"'.V   '■',';"WJ^'-k.?V"!J!kl'i' 


M  ■  .:^ 


active      passiuc. 

Fig.  3. — Indicating  the  conditions  of  the  local  circuit  at  the  boundary  between  the 
active  and  the  passive  areas  of  an  iron  wire  in  nitric  acid;  the  direction  of  the  current 
(positive  stream)  is  indicated  by  the  arrows,  the  active  region  (shaded)  being  anodal,  the 
passive  cathodal.  The  local  intensity  of  the  current  in  the  passive  region  (and  hence  the 
reducing  or  activating  effectiveness)  decreases  in  the  order  A  <B<C;  beyond  a  certain 
distance  from  the  boundary,  e.g.,  XV,  it  will  be  insufficient  to  activate. 

over  a  certain  area  (usually  cathodal,  e.g.,  XY,  Fig.  3), 
adjoining  •  the  boundary  between  the  two  regions,  and 
the  similar  circuit  which  is  then  formed  at  the  boundary 
between  the  newly  altered  area  and  the  unaltered  area 
beyond  repeats  the  effect;  hence  the  alteration  auto- 
matically spreads  over  the  whole  surface.  A  wave  of 
such  transmission  is  necessarily  associated  with  a  wave 
of  electromotor  variation. 

A  brief  account  of  the  phenomena  of  activation  and 
transmission  in  passive  iron  will  imhcate  more  clearly 

'  American  Journal  of  Physiology,  XLI  (19 16),  126;  ScictKc,  XLVIII 
(1918),  51;  L  (1919),  259,  416;  Journal  of  Physical  Chemistry,  XXIV 
(1920),  165;  Jour.  Gen.  Physiol.,  Ill  (1920),  107,  129. 


254   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

the  general  nature  of  such  processes.^  Passivity  is 
readily  induced  in  an  iron  wire  by  immersion  in  strong 
nitric  acid  (sp.  gr.  1.42);  the  metal  then  remains  un- 
altered or  chemically  inactive  when  transferred  to  weak 
acid  (sp.  gr.  1.2),  unless  it  is  artificially  ''activated." 
Activation  may  be  induced  by  various  means,  chemical, 
mechanical,  and  electrical.  The  following  simple  and 
readily  performed  experiments  will  bring  out  clearly 
the  chief  resemblances  between  the  processes  of  activation 
and  transmission  in  the  metallic  systems  and  in  Kving 
protoplasm. 

When  the  passive  iron  wire  is  immersed  in  a  dish  of 
nitric  acid  of  about  60  volumes  per  cent  concentration 
(i.e.,  of  commercial  HNO3  c>f  sp.  gr.  1.42),  no  change 
occurs,  and  the  surface  of  the  metal  remains  bright  and 
unaltered.  If,  however,  it  is  then  touched  with  a  piece 
of  ordinary  ''active"  iron,  or  with  a  base  metal  Hke 
zinc,  a  local  reaction,  accompanied  by  effervescence  and 
a  darkening  of  the  bright  metalHc  surface,  is  at  once 
initiated  and  sweeps  rapidly  over  the  whole  wire  from 
end  to  end.  In  acid  of  the  foregoing  concentration,  the 
local  reaction  ceases  in  one  or  two  seconds  (at  20°),  and 
the  metal  reverts  automatically  to  the  passive  state. 
Immediately  after  this  repassivation  it  is  resistant  to 
activation  and  transmits  the  reaction  imperfectly;  on 
standing,  transmissivity  gradually  returns  and  within 
a  minute  is  usually  again  complete;  the  metal  can  then 
be  activated  as  before  and  the  same  phenomenon  is 
repeated.     The  passive  wire  may  be  activated  mechani- 

^  For  a  general  review  of  the  phenomena  of  passivity  in  metals 
cf.  Bennett  and  Burnham,  Journal  of  Physical  Chemistry,  XXI  (1917), 
107. 


ELECTRICAL  AND  OTHER  FACTORS     255 

cally  by  jarring  or  bending  or  by  scrai)ing  with  a  piece 
of  glass;  summation  effects  arc  a  conspicuous  future  of 
this  form  of  activation;  a  single  scrape  or  blow,  or  a  suc- 
cession of  these  at  infrequent  intervals,  being  usually 
ineffective,  while  several  scrapes  in  rapid  succession  cause 
typical  activation.  Chemical  activation  may  be  shcjwn 
by  the  application  of  a  reducing  agent  hke  sugar.  The 
same  kind  of  effect  is  produced  in  the  wire,  whatever  the 
method  of  activation,  the  local  change  simply  .initiating 
a  propagated  effect  whose  nature  and  extent  depend 
on  the  special  conditions  existing  in  the  metal-electrolyte 
system.  There  is  here  an  evident  analogy  with  explo- 
sions or  other  kinds  of  'trigger  effects."  Hence  the 
system,  when  in  a  fully  transmissive  state,  behaves  in 
the  ^^all-or-none"  manner. 

In  reality  electrical  activation  is  illustrated  in  all 
these  cases,  even  when  the  local  alteration  initiating  the 
reaction  is  mechanical  or  chemical;  i.e.,  the  electrical 
factor  is  the  essential  one  in  the  transmission  of  the 
effect.  The  special  conditions  of  electrical  activation 
are,  however,  best  show^n  by  a  somewhat  different  kind 
of  experimental  arrangement.  Two  passive  wires,  placed 
parallel  one  or  two  centimeters  apart,  are  immersed  in 
a  vessel  containing  dilute  HNO3  and  are  connected  by 
wires  and  an  open  key  to  a  battery  (e.g.,  of  about  2 
volts  E.M.F.).  When  the  key  is  closed,  the  cathodal 
wire  (that  connected  with  the  negative  pole  or  zinc  of 
the  battery)  is  at  once  activated,  while  the  anodal  wire 
remains  unchanged.  This  experiment  shows  that  activa- 
tion is  a  polar  effect  and  dependent  on  cathodal  reduction. 
Activation  also  requires  a  certain  minimal  E.M.F.  in  the 
battery,  usually  exceeding  one  volt,  and  a  certain  minimal 


256    PROTOPLAS]\nC  ACTION  AND  NERVOUS  ACTION 

duration  of  flow  of  the  current.  Electrical  summation- 
effects  similar  to  those  of  mechanical  activation  can  also 
be  demonstrated  under  appropriate  conditions.^ 

Another  influence  of  the  current  is  especially  interest- 
ing from  its  resemblance  to  the  physiological  phenomenon 
of  electrotonus ;  this  consists  in  a  modification  of  the 
susceptibiHty  of  the  wire  to  mechanical  or  other  activa- 
tion. During  the  flow  of  the  current  the  automatic 
return  of  passivity  in  the  active  (cathodal)  wire  is 
delayed,  or  with  sufficient  strength  of  current  prevented, 
and  the  anodal  wire  becomes  more  resistant  to  mechani- 
cal or  other  activation.  If  with  two  passive  wires  in  a 
circuit,  as  above,  a  constant  current  too  weak  to  cause 
activation  under  these  conditions  (e.g.,  the  current  from 
one  Edison  cell)  be  passed,  the  cathodal  wire,  although 
remaining  passive,  is  rendered  temporarily  more  sus- 
ceptible than  before  to  activation  by  other  means, 
e.g.,  mechanical  treatment,  while  the  anodal  wire 
becomes  less  susceptible.^ 

All  of  the  foregoing  phenomena  have  their  parallels  in 
the  behavior  of  Hving  irritable  tissues  under  the  influence 
of  the  electric  current;  the  corresponding  physiological 
phenomena  are  summation,  polar  stimulation,  chronaxie, 
enhancement  of  irritability  near  cathode,  and  its  decrease 

near  anode  ('' electrotonus")- 

Phenomena  of  a  similar  kind  are  seen  in  the  mercury- 
peroxide  system;  here  also  the  inactive  mercury  may 
be  activated  by  making  it  the  cathode  in  a  circuit,  or 

^  E.g.,  by  using  the  brief  contact  of  a  copper  wire  as  an  activating 
agent.  The  local  current  thus  produced  may  be  too  brief  for  activation 
by  a  single  contact,  while  several  contacts  in  close  succession  will  pro- 
duce the  effect. 

=  For  a  somewhat  fuller  description  cf.  Jour.  Gen.  Physiol.,  Ill 
(1920),  136. 


ELECTRICAL  AND  OTHER  FACTORS  257 

the  rhythm  of  an  automatic  pulsation  may  be  altered. 
During  the  flow  of  the  current  the  catalytic  effect  at 
the  cathode  is  heightened,  while  at  the  anode  it  is 
decreased  or  the  rhythm  may  be  abolished.'  The  i)aral- 
leHsm  between  these  effects  and  those  produced  by  the 
constant  current  on  the  action  of  rhythmical  tissues 
hke  the  heart  is  evident. 

A  more  detailed  account  of  the  phenomena  in  film- 
covered  metallic  systems  of  this  kind  is  not  possible 
within  the  limits  of  space,  but  attention  should  be  called 
to  another  interesting  feature  of  the  electrical  initiation 
of  these  reactions.  A  pecuharity  of  the  electrical 
activation  of  passive  iron  is  that  it  is  not  readily  produced 
by  currents  which  rise  slowly  from  a  minimal  strength  to 
a  strength  sufficient  to  activate  with  sudden  closure.^  In 
other  words,  the  rate  of  change  of  the  activating  current 
is  an  essential  factor  in  the  effect  produced.  This  is  a 
well-known  and  highly  characteristic  feature  in  the 
response  of  living  tissues  to  electrical  activation.  Each 
tissue  has  its  characteristic  time-factor  of  electrical  excita- 
tion or  so-called  ''chronaxie,"  and  this  is  closely  related 
to  the  rate  of  change  required  of  a  stimulating  current 
(cf.  p.  288).  The  time-relations  of  the  activating  current 
in  the  metalKc  system  resemble  those  in  livinp:  tissues 
in  the  further  respect  that  in  the  case  of  alternating 
currents  the  relation  between  the  intensity  required 
for  activation  and  the  rate  of  alternation  follows  the 
same  law,  as  shown  by  Bredig  and  Kerb  for  the  mercury 
H2O2  system  ;3    that  is,  there  is  an  inverse  relation  bc- 

^  Bredig  and  Wilke,  Biochcm.  Zeitschrift,  XI  (1908),  67. 
'Science,  XLVIII  (1918),  57- 

3  Bredig  and  Kerb,  Verh.  naturhisiorisch-mcd.  Verrins  zu  llfidfl- 
berg,  X  (1909),  N.F.,  23. 


258    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

tween  the  intensity  required  to  activate  and  the  root  of 
the  number  of  alterations  {i/\/n  =  const.).  This  relation 
has  been  shown  by  Nernst^  and  others  to  be  generally 
characteristic  of  electrical  excitation  in  H\dng  tissues; 
it  indicates  that  a  current  of  a  given  intensity  must  flow 
for  a  certain  minimal  time  in  one  direction  through  the 
irritable  system  in  order  to  cause  activation.  I.e.,  the 
change  in  the  electrical  polarization  of  the  surface  con- 
cerned in  activation  must  last  for  more  than  a  certain 
critical  time,  presumably  the  time  necessary  to  produce 
a  certain  critical  degree  of  chemical  change.  The 
physical  conditions  of  response  to  electrical  influence 
thus  appear  to  be  of  the  same  kind  in  the  living  system 
and  in  the  inorganic  model. 

^  Nernst,  Arch.  ges.  Physiol.,  CXII  (1908),  275;  cf.  chap.  xii. 


CHAPTER  XII 

STIMULATION  AND  TRANSMISSION  OF  EXCITATION 

IN  PROTOPLAS:\I 

Responsiveness  to  stimulation  is  a  universal  character- 
istic of  living  matter.  Typically  the  reaction  to  a 
stimulus  involves  a  performance  of  work  (i.e.,  trans- 
formation of  energy)  which  has  no  definable  proportion 
to  the  work  done  by  the  stimulating  agent  upon  the 
living  system.  The  stimulus  usually  acts  locally,  yet 
the  whole  living  system — cell,  tissue,  or  even  entire 
organism — may  be  thrown  into  activity.  Transmission 
of  physiological  influence  from  the  immediate  site  of 
stimulation  to  other  regions  of  the  living  system  is 
thus  a  constant  feature  of  stimulation.  Hence  the 
subject  of  the  essential  conditions  determining  this 
transmission  is  one  of  fundamental  biological  interest; 
evidently  the  living  system  can  react  as  a  whole,  i.e.,  in 
a  unified  or  correlated  manner,  only  in  so  far  as  the 
physiological  processes  in  any  single  region  occur  in 
correlation  with  those  in  other  regions.  This  trans- 
missive  property  of  protoplasm  is  the  primary  integrative 
factor  in  organisms;  its  highest  development  has  been 
attained  in  the  nervous  system  of  higher  animals.^ 

In  general,  local  variations  in  protoplasmic  activity, 
implying  variations  in  the  rate  or  character  of  the 
underlying  chemical  or  metabolic  processes,  influence 
other  processes  occurring  at  a  distance  from  the  active 

^  Cf.  my  review  of  the  subject  of  protoplasmic  transmission  in 
Physiological  Reviews,  II  (1922),  i. 

259 


26o    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

« 

region.  The  physical  constitution  of  the  living  substance 
is  evidently  of  such  a  nature  as  to  permit  rapid  trans- 
mission of  chemical  influence  to  a  distance;  in  other 
words,  some  form  of  '' chemical  distance-action"  is  a 
constant  feature  of  protoplasmic  action.  It  is  natural 
to  connect  this  feature  with  the  essential  or  fundamental 
features  of  the  physical  structure  of  protoplasm.  We 
have  already  seen  that  this  structure  is  polyphasic  and 
film-pervaded,  or  emulsion-like.  It  is  therefore  highly 
interesting  to  note  that  the  inorganic  transmissive 
processes  just  considered,  which  bear  such  a  striking 
resemblance  to  the  transmissive  processes  of  protoplasm, 
are  in  fact  determined  by  chemical  and  structural 
alterations  in  thin  surface-films,  and  that  these  alterations 
occur  under  the  influence  of  local  electric  circuits.  In 
such  a  system  as  passive  iron  in  nitric  acid  the  chemically 
reactive  material  whose  alteration  determines  the 
transmission  is  spread  out  in  a  thin  layer  or  film  at  an 
interface  (metal-electrolyte)  which  is  the  seat  of  a 
potential  difference.  The  surface  of  contact  of  this 
material  with  the  adjacent  layer  of  electrolyte  solution 
is  a  large  one,  relatively  to  the  total  mass  of  reacting 
substance.  This  arrangement  makes  for  a  rapidly 
acting  and  sensitive  type  of  reaction-system,  since  the 
removal  or  alteration  of  a  very  small  quantity  of  material 
may,  by  altering  electromotor  conditions  at  the  surface, 
form  the  condition  for  a  spread  of  chemical  effect, 
electrically  conditioned,  which  may  be  very  extensive 
and  rapid. ^     Transmission  depends  on  the  instantaneous 

^It  may  be  pointed  out  here  that  the  importance  of  extremely 
small  quantities  of  certain  special  substances,  e.g.,  vitamines  in  animals, 
is  probably  a  correlative  of  the  control  of  chemical  reactions  in  protoplasm 


STIMULATION  AND  TRANSMISSION  261 

passage  of  an  electric  current  throu^^h  the  circuit  con- 
stituted by  the  two  chemically  or  structurally  ch'tTerent 
portions  of  this  thin  interfacial  film,  together  with  the 
electrically  conducting  phases  (in  this  case  metal  and 
nitric  acid)  between  which  it  is  interposed.  In  li\in^' 
protoplasm,  with  its  film-partitioned  constitution,  it 
seems  probable  that  the  structural  arrangement  or 
disposition  of  the  chemically  reactive  material  which 
determines  the  response  to  stimulation  is  of  a  simihir 
kind;  i.e.,  that  this  material  is  disposed  in  the  form  of  a 
thin  film  between  two  electrically  conducting  phases, 
a  type  of  arrangement  allowing  transmissions  to  occur 
under  conditions  of  essentially  the  same  physical  kind 
as  in  the  foregoing  inorganic  type  of  system. 

It  has  already  been  pointed  out  that  stimulation 
processes  cannot  be  considered  separately  from  the 
processes  of  transmission  or  conduction.  In  general  the 
effects  of  local  alteration  in  protoplasm  tend  to  spread; 
i.e.,  to  produce  chemical  and  physiological  effects  in 
other  regions  than  those  immediately  acted  upon  by  the 
stimulating  agent.  In  some  cases  this  spread  is  limited 
in  extent;  but  in  others,  especially  nerve,  there  appears 
to  be  no  limit  to  the  distance  through  which  the  change 
of  activity  may  be  transmitted.  Hence  the  total  effect 
of  any  stimulation  has  no  fixed  relation,  quantitative  or 
qualitative,  to  the  direct  physical  effect  produced  by 
the    stimulus    at    its   point    of    application.     In    many 


by  film-structure.  When  material  is  in  a  film,  small  quantities  may 
determine  large  chemical  efi^ects,  because  under  these  conditions  what 
is  important  is  not  so  much  the  quantity  of  material  as  tlic  area  which 
it  covers.  Surface  relations  rather  than  mass  or  volume  relations  then 
become  the  controlling  factor. 


262    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

irritable  systems  with  highly  developed  transmissive 
properties,  e.g.,  the  nerve  fibers  and  muscle  cells  of 
higher  organisms,  the  character  and  intensity  of  the 
response  are  quite  independent  of  those  of  the  stimulus, 
provided  the  latter  attains  the  threshold  value.  A  full 
response,  involving  the  whole  irritable  element,  results 
from  either  a  'Sveak"  or  a  "strong"  stimulus;  this  is 
the  ''all  or  none"  type  of  behavior,  which  is  found  also 
in  many  physical  systems  in  unstable  equilibrium,  and 
also  in  explosive  systems  or  others  in  which  chemical 
change  is  rapidly  transmitted;  e.g.,  the  passive  iron 
system.  In  all  such  cases  there  is  a  ''release"  of  stored 
energy,  and  the  work  performed  by  the  releasing  agent 
has  no  definite  relation  to  the  energy  transformed  in 
the  resulting  process.^ 

The  phenomena  of  stimulation  in  living  organisms 
are  so  various  that  one  hesitates  to  regard  them  all  as 
determined  by  conditions  of  the  same  physico-chemical 
kind.  Nevertheless,  it  is  a  striking  fact  that  whatever 
the  special  peculiarities  of  the  organic  activity  or  response 
in  different  living  systems  may  be,  the  conditions  of 
initiation  and  control  are  remarkably  uniform.  The 
universal  susceptibility  to  the  electric  current,  to  mechani- 
cal disturbance,  and  to  certain  kinds  of  chemical  influ- 
ence, especially  the  influence  of  inorganic  salts  and  the 
lipoid-solvent  or  surface-active  group  of  organic  com- 
pounds, indicates  that  the  fundamental  structural  and 
chemical  conditions  underlying  the  response  to  stimula- 
tion are  the  same  in  all  forms  of  protoplasm.     It  is 

*  The  typical  case  is  one  of  "trigger  action,"  which  is  a  characteristic 
feature  of  all  modes  of  organic  response  (cf .  the  interesting  discussion  of 
Lotka:  "Natural  Selection  as  a  Physical  Principle,"  Proceedings  of  the 
National  Academy  of  Science,  VIII  [1922],  151). 


STIMULATION  AND  TRANSMISSION  263 

especially  to  be  noted  that  the  two  of  the  most  general 
features  of  stimulation-processes,  viz.,  the  susceptibihty 
to  the  electric  current,  and  the  reversible  modification  or 
suppression  of  irritability  by  the  surface-active  groups 
of  compounds  (amesthesia  or  narcosis),  indicate  definitely 
a  dependence  of  protoplasmic  activity  on  the  polyphasic 
structure  of  the  system.  The  inference  from  such  facts 
is  that  the  chemical  reactions  of  protoplasm  are  controlled 
by  the  peculiar  conditions  resident  at  the  protoplasmic 
interfaces  or  phase-boundaries;  and  the  resemblance 
between  the  conditions  of  activity  of  irritable  proto- 
plasmic systems  and  of  the  inorganic  models  just 
described  confirms  this  inference. 

Some  of  the  more  general  features  of  the  phenomena 
of  stimulation  in  living  organisms  have  already  been 
discussed  briefly.  Since  continued  life  depends  on  a 
regulated  interchange  of  material  and  energy  with  the 
environment,  it  is  to  be  assumed  that  all  fundamental 
vital  activities  are  capable  of  varying  in  correlation 
with,  or  ''in  response  to,"  environmental  change;  the 
character  and  rate  of  the  interaction  of  the  living  system 
with  its  environment  are  thus  controlled.  Normally 
the  responses  of  any  organism  to  stimulation  are  of  such 
a  kind  as  to  favor  its  continued  or  stable  existence  in 
this  environment.  A  certain  difficulty  in  defining  the 
conception  of  stimulation  arises  here,  since  many  cases 
exist  where  physiological  activities,  which  in  themsch'es 
are  injurious  or  destructive  to  the  living  system  as  a 
whole,  may  be  induced  by  environmental  change;^  such 

^  The  oxidation  rate  of  sea-urchin  eggs  may  be  increased  l)y  pure 
NaCl  solution  to  a  degree  which  apparently  is  directly  destrucli\e. 
The  case  of  fatigue  carried  to  an  injurious  extreme  is  analogous. 


264    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

instances  would  scarcely  be  classed  as  responses  to 
stimulation.  In  fact  many  opportunities  for  verbal 
mystification  arise  in  attempting  to  '' define"  the  concept 
''stimulation."  In  order  to  limit  the  following  discus- 
sion, we  shall  regard  as  a  ''stimulus"  any  influence 
acting  from  without  upon  the  living  system  which  changes 
the  rate  or  the  character  of  the  normal  vital  activities; 
the  resulting  change  of  physiological  activity  is  the 
"response."  Even  with  this  simplified  conception,  the 
range  of  phenomena  is  still  too  great  to  be  readily 
included  under  any  strictly  drawn  definition;  but  such 
a  definition  need  not  be  insisted  upon,  provided  the 
general  nature  of  the  relations  between  organism  and 
environment  is  clearly  understood.  Variation  of  vital 
activity,  within  the  physiological  range,  occurring  as  a 
constant  correlative  or  sequence  of  environmental 
change  of  some  kind,  is  the  essential  phenomenon 
whose  conditions  we  are  considering. 

In  multicellular  organisms,  "internal"  and  "external" 
(proprioceptive  and  exteroceptive)  stimuli  are  often 
distinguished,^  since  in  many  cases  the  environment 
which  furnishes  the  normal  stimuli  for  an  irritable  cell 
or  cell-system  may  be  not  the  external  world  but  some 
other  part  of  the  same  organism.  Responses  of  special 
organs  or  organ-systems  to  stimuli  originating  else- 
where within  the  same  organism  form,  in  fact,  a 
regular  part  of  many  normal  physiological  cycles  in 
higher  animals;  thus  the  pancreas  is  stimulated  by 
secretin  in  the  blood  stream,  and  the  respiratory 
center  by  increased  H-ion  concentration  of  the  blood; 
the  central  nervous  system  is  continually  adjusting  its 

*  Cf.  Sherrington,  Integrative  Action  of  the  Nervous  System. 


STIMULATION  AND  TRANS.MISSION  265 

activity  to  changes  in  bodily  conditions,  and  so  on. 
Evidently  the  effects  of  external  stimuli  upon  the  sense 
organs  cannot  be  regarded  as  forming  a  significanlly 
different  class  from  these  phenomena,  so  that  from  the 
standpoint  of  general  physiology  the  foregoing  distinc- 
tion is  a  purely  formal  one  and  has  lit  lie  objective 
importance. 

Various  terms  are  applied  to  special  processes  which 
may  be  included  under  the  general  conception  of  stimula- 
tion, as  just  defined.  The  term  ''activation''  is  used 
with  reference  to  the  initiation  of  development  in  a 
resting  egg  cell  by  a  spermatozoon  or  a  parthenogenetic 
agent;  acceleration,  or  simple  increase  in  the  rate  of  an 
already  existing  process,  is  a  frequent  form  of  response 
(e.g.,  secretion,  the  heart-beat,  or  other  regular  muscular 
movement,  growth,  etc.);  retardation  or  inhibition  is 
perhaps  equally  frequent.  In  cases  of  automatism,  like 
that  of  the  heart,  the  rhythm  may  be  regarded  as  deter- 
mined by  periodic  stimuli  furnished  by  processes  icithin 
the  cell.  Since  all  of  these  phenomena  may  occur,  or 
undergo  modification,  in  response  to  changes  of  cn\iron- 
mental  condition,  all  are  to  be  considered  under  the 
general  conception  of  stimulation. 

The  most  general  features  of  the  stimulation-process 
are  best  studied  in  those  irritable  tissues  or  cells  which 
give  a  prompt  and  definite  response  to  electrical  or 
mechanical  stimulation,  such  as  the  nerves  and  muscles 
of  higher  animals;  and  the  majority  of  investigations, 
on  stimulation,  especially  those  of  a  quantitative  kinil. 
have  been  carried  gut  with  these  tissues,  usually  alter 
isolation.  The  results  gained  have,  however,  a  general 
apphcability  to  other  irritable  living  systems. 


266    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 
GENERAL  CONDITIONS  OF  STIMULATION 

It  is  well  known  that  different  living  systems  may 
vary  widely  in  their  sensitivity  to  the  same  stimuli, 
and  also  that  irritability  is  often  specialized  with  reference 
to  particular  physical  agents.  Sensory  elements  with 
special  sensitivity  to  light,  contact,  slight  changes  of 
temperature,  or  chemical  substances,  are  found  in  all 
higher  animals.  These  differences  are  referred  to  special 
features  of  chemical  and  structural  organization. 
Chemical  sensitivity  in  particular  is  often  minutely 
specialized;  and  such  instances  as  the  special  sensitivity 
exhibited  by  the  sensitized  smooth  muscle  of  guinea-pigs 
in  anaphylaxis  indicate  clearly  that  many  forms  of 
specific  chemical  irritability  are  dependent  on  the 
presence  of  specific  chemical  compounds  (apparently 
in  this  case  proteins)  in  the  irritable  cell,  probably  in 
the  protoplasmic  surface  layer.  Similarly,  photo-sensi- 
tive elements  like  the  retinal  rods  and  cones  contain 
compounds  of  definite  photochemical  properties  (visual 
purple  and  related  substances)  upon  which  the  special 
responsiveness  undoubtedly  depends.^  We  must  recog- 
nize, therefore,  in  addition  to  the  general  susceptibility 
to  mechanical  or  electrical  stimuli  possessed  by  all  forms 
of  protoplasm,  a  variety  of  specific  or  selective  forms  of 
irritability  depending  on  special  features  of  structure  or 
organization.  Selective  irritability  is  shown  especially 
by  the  sensory  nerve-termini  or  receptors  of  higher 
animals;   these  are  classified,  according  to  the  agents  to 

*  Thus  Hecht  and  Williams  have  recently  sho^vn  that  the  curve 
of  absorption  of  visual  purple  is  almost  identical  with  the  curve  of 
visual  sensitivity  for  different  wave-lengths  (Jotir.  Gen.  Physiol. ^  IV 
[1922],  i). 


STIMULATION  AND  TRANSMISSION  267 

which  they  are  specially  responsive,  as  chemo-receptors, 
thermo-receptors,  photo-receptors,  etc. 

Such  special  sensitivity  may  be  described  as  consisting 
in  a  lowering  of  the  threshold  of  stimulation  for  a  particu- 
lar agent,  and  need  not  affect  the  general  sensitivity  to 
mechanical  and  electrical  stimulation.  Some  specific 
irritabihty  is  superposed  upon  the  general  or  non- 
specific irritabihty.  Thus  a  nerve  or  muscle  may  be 
stimulated  by  mechanical,  thermal,  chemical,  osmotic, 
and  electrical  stimuli;  similarly,  a  highly  specialized 
receptor  such  as  a  retinal  element  may  be  stimulated 
by  these  agents  as  well  as  by  light  of  a  definite  wa\e- 
length.  In  all  cases,  however,  the  response  following 
stimulation  has  a  specific  character  which  is  dependent 
on  the  special  structure  or  organization  of  the  irritable 
system  or  on  its  relations  with  other  systems.  In  the 
field  of  sensory  stimulation  this  generalization  is  known 
as  the  "law  of  specific  energies." 

LOCAL  CHANGE  AND  PROPAGATED  EFFECT 

We  have  seen  that  an  irritable  system  with  a  highly 
developed  general  sensitivity,  e.g.,  a  muscle  or  a  nerve, 
may  be  excited  by  a  variety  of  stimulating  agents,  and 
the  question  arises  why  such  physically  dissimilar  agents 
produce  the  same  physiological  effect.  The  general 
sequence  of  events  when  such  a  tissue  is  stimulated  may 
be  briefl^y  described  as  follows.  Some  local  change, 
whose  precise  nature  is  determined  by  the  nature  of  the 
stimulating  agent,  occurs  at  the  site  of  stimulation;  a 
state  of  ''excitation"  is  there  initiated  which,  however, 
does  not  remain  confined  to  this  region,  but  spreads  or 
is  propagated  to  a  distance,  often  at  a  high  velocity. 


268    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

This  propagated  effect,  or  "propagated  disturbance" 
(Keith  Lucas'  term),  as  it  appears  at  a  distance  from 
the  point  of  stimulation,  has  its  own  definite  pecuharities, 
which  are  independent  of  the  nature  of  the  initiatory 
local  change  or  stimulus.  For  example,  any  single  nerve- 
impulse  in  a  normal  frog's  nerve,  by  whatever  means  it 
is  initiated,  travels  at  a  constant  velocity  (assuming  the 
state  of  the  tissue  to  be  normal  and  the  temperature  and 
surrounding  conditions  constant),  and  its  most  readily 
observed  physical  accompaniment,  the  bioelectric  varia- 
tion, has  a  definite  range  of  potential  change  and  definite 
time-relations.  In  other  words,  the  propagated  dis- 
turbance differs  from  the  local  change  in  exhibiting 
constant  and  specific  features,  qualitative  and  quantita- 
tive, whose  nature  is  determined  by  the  special  or 
inherited  constitution  of  the  tissue. 

Almost  any  kind  of  sufficiently  rapid  local  alteration 
may  initiate  such  a  wave  of  physical  and  chemical 
disturbance.  The  distinction  between  the  local  change 
and  the  propagated  effect  is  a  fundamental  one  in  any 
theory  of  stimulation.  The  former  is  the  ''releasing" 
event  and  follows  upon  some  simple  physical  change 
produced  in  the  tissue  by  the  stimulating  agent;  the 
latter  is  the  distinctively  physiological  process,  and  as 
such  has  specific  characters  of  a  complex  kind,  dependent 
on  the  nature  of  the  irritable  system  and  as  yet 
imperfectly  analyzed. 

Especially  significant  is  the  fact  that  all  irritable 
elements,  apparently  without  exception,  respond  to 
electrical  stimuli,  or  are  influenced  in  their  already 
existing  activity  by  the  electric  current.  The  electrical 
sensitivity  of  highly  irritable  tissues,  such  as  vertebrate 


STIMULATION  AND  TRANSMISSION  269 

motor  nerve,  is  extreme;  the  frog's  sciatic  nen-c  may 
be  stimulated  by  a  current  of  .000001  ampere  or  less; 
it  is  well  known  that  the  neuro-muscular  ai)paratus  of 
the  frog  was  used  by  Galvani  as  the  most  sensiti\e 
means  known  to  hmi  by  detecting  variations  in  the 
electrical  state  of  bodies;  in  fact  it  is  to  this  property  of 
living  tissues  that  we  owe  the  discovery  of  current 
electricity  by  Volta.  Galvani's  experiments  also  showed 
^although  their  significance  was  disputed  at  the  time — 
that  electric  currents  are  produced  in  the  activity  of 
living  tissues.  Thus  two  of  the  most  fundamental 
properties  of  living  matter,  its  electrical  sensitivity,  and 
its  production  of  electrical  currents  during  activity, 
were  early  observed;  and  many  of  the  chief  problems 
of  general  physiology  at  the  present  time  relate  to  the 
physico-chemical  conditions  and  physiological  signifi- 
cance of  these  properties.  That  they  are  among  the 
chief  factors  controlling  normal  cell-processes  seems 
certain. 

NATURE  OF  THE  LOCAL  CHANGE 

It  is  remarkable  that  complete  stimulation,  involving 
a  change  in  the  activity  of  the  entire  cell,  is  produced 
in  many  if  not  all  irritable  elements  by  agents  which 
affect  directly  only  the  surface-layer  of  i)rotoj)lasm. 
Some  local  modification  of  surface  conditions  seems  to 
be  all  that  is  required  to  set  in  motion  the  whole  complex 
process  of  stimulation.  This  is  best  shown  in  the 
mechanical  stimulation  of  single  cells;  thus  in  a  ciliated 
protozoon  like  Paramoeciiim  a  slight  IoikH  is  suflicient 
to  call  forth  the  characteristic  motor  reaction,  involving 
a  reversal  of  the  direction  of  ciliary  activity  over  the 
whole    surface    of    the    organism.     The    cxtraordinar>' 


270    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

sensitivity  of  many  blood  cells  to  mechanical  contact 
illustrates  the  same  phenomenon;  a  slight  touch  with  a 
capillary  needle  is  often  sufficient  to  cause  a  rapid  and 
complete  disintegration  of  a  leucocyte  or  a  red  blood 
corpuscle;^  i.e.,  a  wave  of  alteration  involving  the 
breakdown  of  the  semi-permeable  surface-film  is  propa- 
gated over  the  entire  protoplasmic  surface.  The  break- 
down of  the  explosive  corpuscles  in  Crustacea^  and  of 
nematocytes  in  coelenterates  are  other  examples  of  the 
same  kind  of  process.  Such  facts  suggest  that  in  normal 
cases  of  stimulation,  as  in  nerve,  where  a  local  stimulus 
initiates  a  temporary  disturbance,  which  passes  like  a 
wave  over  the  entire  irritable  element,  a  similar  disinte- 
gration of  the  surface-protoplasm  occurs,  with  the  differ- 
ence that  this  change  is  immediately  and  rapidly  reversed 
by  the  formation  of  a  new  surface  layer. 

That  some  such  process  occurs  during  the  transmis- 
sion of  the  excitation-wave  in  a  nerve  or  other  irritable 
tissue  is  indicated  by  the  character  of  the  local  bio- 
electric variation.  A  reversible  surface-change  is 
known  to  accompany  the  transmission  of  the  activation- 
wave  along  a  passive  iron  wire  immersed  in  nitric  acid; 
the  passivating  surface-film  is  removed  by  electrolytic 
reduction  in  the  neighborhood  of  each  active  area,  and 
is  then  immediately  reformed  by  the  oxidizing  action  of 
the  acid  and  of  the  local  electric  current  (at  the  anodal 
areas);  and  the  destruction  and  re-formation  of  the 
film  are  associated  with  definite  and  rapid  variations 
of  potential.     In  the  stimulated  living  system  a  similar 

^  Cf.  Chambers,  Anatomical  Record,  X  (1916),  190. 

^  Cf.  Hardy,  Journal  of  Physiology,  XIII  (1892),  165;  Tait,  Quarterly 
Journal  of  Experimental  Physiology,  XII  (1918),  42. 


STIMULATION  AND  TR.\NSMISSION  2  7 1 

reversible  variation  of  potential  accom])anies  the  passage 
of  the  excitation-wave.  The  resemblance  of  the  trans- 
mission phenomenon  in  passive  iron  to  the  protoplasmic 
type  of  transmission  is  in  fact  so  detailed  as  to  confirm 
strongly  the  hypothesis  that  in  the  latter  case  also  the 
essential  feature  of  the  transmission-i)rocess  is  the 
breakdown  and  reconstruction  of  the  thin  protoplasmic 
surface-film  under  the  influence  of  the  local  bioelectric 
circuits. 

If  the  processes  in  the  living  system  and  in  the  simple 
inorganic  model  are  in  fact  similar  in  their  dependence 
on  surface-changes  of  this  kind,  it  becomes  evident  at 
once  why  protoplasm  is  so  readily  excited  by  conditions 
acting  upon  its  surface  layer.  A  mechanical  agent, 
by  interrupting  the  continuity  of  the  surface-film,  or  by 
otherwise  altering  it  so  as  to  give  rise  to  a  local  circuit, 
may  initiate  a  wave  of  electromotor  variation  and 
disintegration  which  travels  automatically  over  the  whole 
surface,  and  in  so  doing  alters  the  physiological  acti\ity 
of  the  whole  system.  Any  other  sufticient  local  altera- 
tion (chemical,  thermal,  etc.)  may  produce  the  same 
effect.  The  critical  factor  in  the  local  process  of  excita- 
tion thus  appears  to  be  the  alteration  of  the  protoplasmic 
surface-film  in  such  a  manner  as  to  change  locally  the 
potential  difference  between  the  protoplasm  and  the 
external  medium,  to  a  sufficient  degree  and  at  a  sutlicient 
rate.  The  local  circuit  arising  between  this  altered 
region  and  the  as  yet  unaltered  regions  adjoining  forms 
the  next  link  in  the  chain  of  events;  and  if  this  local 
current  has  sufficient  intensity  and  local  density  to 
break  down  electrolytically  the  film  over  a  certain  area 
of  the  adjoining  region,  an  indefinite  wave  of  propagation 


272    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

may  be  initiated,  since  the  same  effect  will  be  repeated 
at  each  newly  formed  boundary  between  the  active  and 
the  inactive  areas. 

According  to  this  conception  the  primary  action  of  a 
local  stimulating  agent  is  to  change  rapidly  the  electrical 
condition  of  the  cell-surface  at  its  point  of  application. 
The  parallel  between  the  irritable  protoplasmic  system 
and  the  passive  iron  model  is  obvious,  since  in  the  latter 
case  also  a  local  alteration  of  the  surface-fihn  involving 
a  local  change  of  potential  is  the  initiating  condition  for 
the  propagated  wave  of  chemical  and  electromotor 
disturbance. 

The  present  view^,  therefore,  regards  stimulation  as 
conditioned  by  surface  processes  of  the  foregoing  def- 
inite kind.  If  this  is  true,  the  structural  arrangements 
providing  for  the  transfer  of  excitation  from  one  irritable 
element  to  another  should  exhibit  features  of  a  character 
to  correspond.  In  fact,  many  peculiarities  of  the 
structure  of  the  central  nervous  system — especially  of 
the  synaptic  junctions — and  of  the  structure  and  arrange- 
ment of  nerve-endings,  such  as  the  myoneural  junctions, 
are  in  harmony  with  this  conception.  Nerve  end-plates 
spread  out  over  the  surface  of  the  muscle  cell,  effecting 
intimate  contact  but  not  penetrating;  the  junctions 
betw^een  neurones  are  effected  by  brushlike  interlacing 
terminals,  or  by  end-feet  and  similar  structures  which 
are  applied  to  the  cell  surface  with  a  closeness  that 
apparently  admits  of  variation.  That  transmission  by 
contact,  through  the  influence  which  the  cell-process 
exerts  upon  adjoining  processes  or  upon  the  cell  body, 
is  the  chief  mode  of  transmission  in  the  nervous  system 
is  one  of  the  corollaries  of  the  neurone  theory  of  the 


STBIULATION  AND  TRANSMISSION  273 

structure  of  this  system.  The  well-known  experiments 
C'rheoscopic  frog")  in  which  one  active  muscle  or  nt-rve 
stimulates  another  which  is  in  close  contact  with  it, 
by  means  of  the  bioelectric  currents  accompanying 
activity,  show  that  excitation  can  be  transmitted  from 
one  irritable  element  to  another  without  direct  proto- 
plasmic continuity,  through  a  purely  electrical  inlluence. 
Similarly  in  the  passive  iron  nitric  acid  system,  activation 
is  readily  transmitted  from  one  wire  to  another  by 
contact,  and  the  basis  of  this  transmission  is  also 
electrical. 

According  to  these  conceptions,  all  forms  of  stimula- 
tion are  electrical;  or,  more  exactly  expressed,  electric 
currents  resulting  from  local  alterations  of  the  cell 
surface  form  a  necessary  part  of  the  sequence  of  processes 
constituting  stimulation.  Such  a  view  imi)lies  further, 
since  the  activity  of  the  whole  cell  is  altered  by  stimula- 
tion— e.g.,  all  of  the  fibrils  in  a  muscle  cell  contract 
when  the  excitation-wave  trav^els  over  its  surface  -  that 
the  intracellular  processes,  including  the  chemical  or 
metabolic  processes  which  furnish  the  energy  for  the 
activity,  are  largely  controlled  by  processes  ha\ing  their 
origin  at  the  cell  surface. 

This  inference  is  confirmed  by  a  study  of  the  contli- 
tions  of  electrical  stimulation.  Hie  work  of  Ncrnst 
and  his  successors'  has  shown  that  the  electric  current 
does  not  act  by  penetrating  the  living  cell  (which  in 
fact  is  a  poor  conductor)  but  by  changing  its  surface- 

^Cf.  Nernst,  GoUingcn  Nachrichtcn,  math.-physik.  Klasse  (1899), 
p.  104;  Arch.  ges.  Physiol,  CXXII  (190S),  275;  Lapicque,  Jour,  de 
Physiol,  IX  (1907),  565,  620;  X  (1908),  601;  XI  (1909),  loog,  1035; 
Lucas,  Journal  of  Physiology,  XL  (1910),  225;  ,\.  \'  Hill,  ibid.,  XL 
(1910),  190. 


274   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

polarization.  And  the  semi-permeability  of  the  plasma 
membranes  of  irritable  cells  (e.g.,  muscle-cells)  with 
reference  to  the  inorganic  salts  of  the  medium — which, 
without  penetrating  the  cell,  nevertheless  influence 
profoundly  its  properties  and  activity — shows  further 
how  closely  cellular  activities  are  dependent  on  surface- 
conditions.  Among  these  surface-conditions  the  state 
of  electrical  polarization  appears  to  be  of  primary 
importance. 

The  facts  of  electrical  stimulation,  now  to  be  con- 
sidered, show  that  variations  in  electrical  surface- 
polarization  have  a  far-reaching  control  over  the  meta- 
bolic and  other  processes  occurring  in  the  cell  interior. 
The  means  by  which  this  polarization  may  be  altered 
are  of  three  chief  kinds:  (i)  changes  in  the  structure  or 
composition  or  permeability  of  the  surface-film;  (2) 
external  electrical  influences,  especially  the  influence  of 
electric  currents  traversing  the  cell  or  its  medium;  and 
(3)  changes  in  the  composition  of  the  medium  or  internal 
protoplasm.  Since,  according  to  the  present  view,  an 
inseparable  feature  of  stimulation,  the  transmission  of 
the  excitation-state,  is  a  direct  result  of  electrical  activa- 
tion by  the  currents  of  local  bioelectric  circuits,  it  is 
clear  that  the  problem  of  stimulation  resolves  itself 
largely  into  the  problem  of  the  general  conditions  under 
which  the  electric  current  stimulates  living  matter. 
Electrical  stimulation  is  in  fact  the  primary  form  of 
stimulation. 

CONDITIONS  OF  ELECTRICAL  STIMULATION 

In  general  the  physiological  studies  of  the  last  two 
decades  have  shown  that  the  stimulation  of  an  irritable 


STIMULATION  AND  TRANSMISSION  275 

living  system  by  the  constant  electric  current  is  subject 
to  definite  quantitative  laws;  they  indicate  also  that 
the  current  acts  primarily  through  its  polarizing  action. 
Upon  this  polarizing  action  follows  chemical  action  as  a 
secondary  consequence. 

The  essential  conditions  under  which  the  current 
causes  stimulation  may  be  briefly  summarized  as 
follows : 

1.  The  current  must  exceed  a  certain  minimal 
intensity;  this  "threshold"  intensity  varies  widely  for 
different  irritable  tissues  and  for  the  same  tissue  under 
different  conditions;  e.g.,  during  states  of  fatigue, 
narcosis,  sensitization,  etc. 

2.  A  current  of  threshold  or  greater  intensity  must 
traverse  the  tissue  for  a  certain  minimal  time;  its 
stimulating  action  thus  depends  not  only  upon  its 
intensity  but  also  upon  the  duration  of  its  flow.  The 
rule  that  for  equal  stimulating  action  the  product  of  the 
intensity  into  the  root  of  the  duration  is  constant 
{i\/t  =  K)  appears  to  hold  for  most  tissues  within  a 
considerable  range  of  intensities.^  For  the  current 
of  threshold  intensity  this  critical  duration  varies  widely 
in  different  tissues  (from  a  few  thousandths  to  several 
seconds) ;  it  is  the  expression  of  a  time-factor  (chronaxie), 
which  is  specific  for  the  tissue  in  question.'' 

These  general  statements  apply  to  the  case  of  currents 
which  reach  their  full  intensity  rapidly  or  instantane- 
ously; e.g.,  when  the  stimulating  circuit  is  suddenly 
closed.  Such  a  condition,  however,  is  apparently  not 
a  normal  or  ''physiological"  one,  since  the  bioelectric 
current — which,  according  to  our  present  conception,  is 

^  C£.  Nernst,  loc.  cit.  '  Cf.  Lapicquc,  Ice.  cU.  (1909). 


276   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

the  factor  arousing  the  local  excitation  at  each  successive 
region  in  a  transmitting  element  (nerve,  etc.) — attains 
its  full  intensity  not  instantaneously  but  in  a  rising 
curve  of  more  or  less  gradual  slope,  varying  from  tissue 
to  tissue,  and  subsides  in  a  similar  manner.  Stimulation 
by  currents  of  varying  intensity  is  thus  the  typical 
condition  prevailing  in  the  organism,  and  to  which, 
therefore,  especial  attention  must  be  directed.  The 
general  empirical  rule  governing  the  action  of  such 
currents  is  as  follows: 

3.  In  order  to  stimulate,  a  current  rising  continuously 

and  uniformly  from  zero  to  full  intensity  must  change 

its  intensity  at  a  certain  minimal  rate  which  is  charac- 

Ai 
teristic    for    the     tissue;     i.e.,     —=  const,    (assuming 

temperature  and  other  conditions  normal).  Hence  we 
find  that  a  slowly  mcreasing  current  may  fail  to  stimulate, 
while  one  rising  to  the  same  intensity  at  a  more  rapid 
rate  stimulates.  The  same  rule  applies  to  stimulation 
by  the  decrease  of  a  current  already  flowing  through 
a  tissue.  The  rate  of  change,  in  either  direction,  must 
exceed  a  minimal  value  which  is  specific  for  the  tissue. 
A  time-factor  enters,  closely  related  to  that  already 
referred  to  above  (under  2)  as  ''chronaxie." 

4.  The  stimulating  action  of  the  current  is  charac- 
teristically polar;  i.e.,  the  current  produces  its  primary 
physiological  effects  chiefly  at  its  regions  of  entrance  and 
exit,  and  the  effects  at  the  two  regions  are  typically 
opposite  or  antagonistic.  Typically,  when  the  current 
is  made,  it  initiates  excitation  at  the  cathode  (i.e.,  where 
the  positive  stream  of  the  stimulating  circuit  passes 
from  the  tissue  to  the  applied  electrode),  and  inhibits 


STIMULATION  AND  TRANSMISSION  277 

activity  (at  the  same  time  depressing  irritability)  at 
the  anode.  When  a  current  already  flowing  through 
the  tissue  is  broken,  stimulation  also  results,  but  the 
polar  relations  are  reversed;  i.e.,  stimulation  is  then  at 
the  anode,  inhibition  at  the  cathode.  'J^his  summarized 
statement  is  the  usual  form  of  the  ''law  of  polar  stimula- 
tion." It  is  important  to  note,  however,  that  a  polar 
action  is  seen  in  many  other  physiological  processes 
occurring  under  the  influence  of  the  current;  e.g., 
electrotonus,  polar  disintegration  of  cells,  galvanotropic 
growth,  and  galvanotaxis.  All  of  these  phenomena  show 
that  the  direction  of  the  current,  relatively  to  the  cell 
surface,  determines  the  nature  of  its  physiological  action. 
The  parallel  to  electrolysis,  at  the  surface  of  any  electrode, 
is  especially  clear  in  phenomena  of  this  class;  it  is  well 
known  that  where  the  positive  stream  passes  from  the 
metallic  electrode  to  the  solution  (at  the  anode)  it 
produces  chemical  effects  (in  general  of  an  oxidative 
kind)  of  the  reverse  nature  to  those  produced  where  it 
passes  from  solution  to  electrode  (cathode);  here  the 
general  chemical  action  is  reducing. 

5.  That  a  variation  in  the  electrical  state  of  the 
irritable  elements,  sufficient  in  degree  and  rate,  is  the 
determining  factor  in  the  physiological  action  of  the 
current  is  seen  in  the  fact  that  a  change  in  either  direction, 
i.e.,  make  or  break,  increase  or  decrease,  may  stimulate 
or  produce  other  characteristic  physiological  elTects. 

6.  Finally,  summation  efl'ects  are  highly  character- 
istic; i.e.,  two  or  more  electric  stimuli  (induction  shocks) 
which,  acting  singly,  are  ineffective,  may  cause  stimula- 
tion if  sent  in  sufficiently  rapid  succession  into  the  tissue. 
The  inter\^al  between  the  successive  single  stimuli  must 


278    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

be  less  than  a  certain  critical  time,  or  no  summation 
results.  This  ''summation  time"  is  closely  related  to 
the  characteristic  time-factor  of  the  tissue,  being  brief 
in  tissue  with  brief  chronaxie  and  vice  versa/  Since  the 
stimuli  normally  acting  in  the  intact  organism  are  largely 
repetitive  or  rhythmical,  summation  processes  are  of 
special  physiological  interest. 

An  exhaustive  discussion  of  the  effects  of  electricity 
on  living  organisms  is  not  possible  within  the  limits  of 
space;  but  those  features  of  electrical  stimulation  which 
indicate  its  dependence  on  surface-alteration  are  of 
fundamental  theoretical  significance  and  will  be  con- 
sidered in  some  detail. 

Chief  among  these  features  are  the  time-relations  of 
electrical  stimulation.  A  stimulating  current  of  a  given 
intensity  must  flow  uninterruptedly  for  more  than  a 
certain  time  through  the  tissue  or  it  produces  no  apparent 
effect.  When  the  relations  between  the  intensity  of  a 
stimulating  current  and  its  minimal  duration  are  investi- 
gated, a  highly  characteristic  relation  appears,  indicating 
that  the  action  of  the  current  depends  upon  the  transport 
of  ions  to  or  from  the  semi-permeable  surfaces  of  the 
irritable  tissue.  The  resulting  change  of  electrical 
surface-polarization  forms  the  primary  condition  of 
stimulation.  This  was  first  clearly  shown  by  Nernst,^ 
in  a  paper  on  the  relation  between  the  stimulating 
action  of  alternating  currents  and  the  rate  of  alternation. 
In  a  living  tissue,  which,  considered  from  a  simplified 
physico-chemical  point  of  view,  represents  an  electrolyte 
solution  partitioned  by  membranes  not  readily  permeable 

^  Cf.  K.  Lucas,  Journal  of  Physiology,  XXXIX  (1910),  461. 
^Nernst,  loc.  cit.  (1899). 


STIMULATION  AND  TRANSMISSION  279 

to  ions,  there  is  during  the  flow  of  the  current  a  movement 
of  cations  with  the  positive  stream  and  of  anions  with 
the  negative  stream;  at  the  semi-permealjle  membranes 
interposed  in  their  path  the  movement  of  ions  is  impeded ; 
the  cations  then  undergo  an  increase  of  concentration  at 
those  surfaces  of  the  membranes  which  face  toward  the 
anode,  simultaneously  with  a  decrease  of  concentration 
at  the  opposite  faces;  the  reverse  relations  hold  with 
the  anions.  A  gradient  of  ionic  concentration  is  thus 
set  up  between  the  layer  of  solution  in  immediate  contact 
with  the  membrane  and  the  layer  at  some  distance. 
This  process  of  concentration  at  the  semi-permeable 
surface  continues  until  a  condition  of  ec|uilibrium  is 
reached  at  which  the  rate  of  diffusion  back  from  the 
membrane  into  the  interior  of  the  solution  is  equal  to 
the  rate  at  which  the  ions  are  transported  to  the  mem- 
brane. Assuming  the  existence  of  these  two  opposed 
processes,  transport  to  the  surface  by  current  and  back- 
diffusion,  it  can  be  shown  that  to  produce  a  dcfmite 
change  in  concentration  at  the  surface,  the  product  of 
the  current-intensity  into  the  root  of  its  time  of  flow 
should  be  constant  (i\^i  =  K). 

This  result  was  reached  by  Xernst  from  the  considera- 
tion of  the  case  of  a  single  membrane  inteqxised  in  the 
path  of  a  current.  It  is  evident  that  sucli  a  system 
offers  conditions  much  simpler  than  those  of  an  irritable 
tissue,  which  typically  consists  of  a  bundle  of  cells  or 
iibrils.  Hill'  and  Keith  Lucas'  have  pointed  out  that 
in  considering  the  case  of  the  living  cell  or  nersx-flber. 
with  its  small  linear  dimensions,  it  is  necessary  to  take 

^Journal  of  Physiology,  XL  (19 10)    190. 
^  Ibid.,  p   225. 


28o   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

into  account  the  processes  at  the  two  opposite  surfaces 
of  each  element,  since  if  these  surfaces  are  close  enough 
together,  there  is  mutual  interference  of  the  two  processes, 
and  more  complex  conditions  have  to  be  assumed.  Yet 
the  fundamental  condition  assumed  by  Nernst's  theory 
— a  membrane  partitioning  an  electrolyte  solution — 
exists  in  the  living  tissue,  hence  polarization  effects  must 
result  when  a  current  is  passed;  and  it  has  been  found 
that  the  foregoing  law  relating  the  current-intensity  to 
the  duration  required  for  a  constant  polarizing  effect  holds 
true  also  for  the  stimulating  effect  of  the  current  within 
a  considerable  range  of  intensities  and  durations,  and 
especially  for  higher  intensities.  This  general  result, 
that  polarizing  effect  and  stimulation  run  closely  parallel, 
indicates  that  stimulation  is  a  consequence  of  the 
polarizing  action  of  the  current. 

Hermann^  and  others  had  previously  referred  the 
stimulating  action  of  the  current  to  its  polarizing  action, 
since  in  any  tissue  the  presence  of  a  reverse  current 
(polarization  current)  can  always  be  demonstrated 
immediately  after  the  passage  of  a  brief  constant  current. 
A  high  degree  of  polarizability  is  characteristic  of  living 
tissues,  and  this  peculiarity  is  undoubtedly  dependent 
on  the  semi-permeable  properties  of  the  cell  membranes, 
since  the  polarization  current  is  greatly  diminished  at 
death,  at  which  time  the  membranes  lose  semi- 
permeability,  as  already  pointed  out.  Both  polariza- 
bility and  semi-permeability  are  thus  manifestations  of 
the  same  condition,  hindrance  to  diffusion  of  ions. 
Lapicque  has  shown  that  the  polarization  currents 
obtained  from  dead  partitions  (parchment  or  bladder 

^  L.  Hermann, FawJJwc/f  der  Physiologie,Leipzig,  II  (1879),  Part  1, 193. 


STIMULATION  AND  TRANSMISSION  281 

membranes)  are  related  to  the  intensity  and  duration  of 
the  polarizing  current  in  the  same  manner  as  the  stimuhi- 
ting  effect  of  a  current  traversing  a  living  irritable  tissue; 
i.e.,  to  produce  a  constant  polarization  current,  the 
product  of  the  intensity  of  the  polarizing  current  into 
the  root  of  its  duration  must  be  constant.^  It  thus 
appears  certain  that  the  primary  or  initiatory  process  in 
electrical  stimulation  is  the  production  of  a  certain 
critical  degree  of  polarization  at  the  semi-permeable 
membranes  of  the  irritable  tissue.  In  other  words,  the 
current  stimulates  by  means  of  its  polarizing  action, 
i.e.,  by  producing  a  potential  difference  (or  by  altering 
an  already  existing  potential  dillerence)  between  the 
external  and  the  internal  faces  of  the  semi-permeable 
plasma  membranes. 

It  should  be  noted  that  in  itself  this  result  throws 
little  light  upon  the  special  physiological  nature  of  the 
stimulation-process;  it  merely  delines  the  physical  con- 
ditions under  which  this  process  is  initiated.  The  process 
itself,  as  just  pointed  out,  has  its  specific  peculiarities 
which  are  independent  of  the  nature  of  the  exciting  agent. 
It  is,  however,  an  important  theoretical  advance  to 
recognize  that  polarization  changes  are  involved  in  all 
forms  of  stimulation.  That  this  is  the  case  is  further 
shown  by  the  invariable  participation  of  bioelectric 
currents  in  stimulation  processes;  these  currents,  like 
any  others  traversing  the  tissue,  must  cause  changes  of 
polarization  at  the  cell  surfaces.  According  to  the 
present  view,  the  spread  of  excitation  is  due  to  the 
secondary  stimulation-effects  resulting  from  the  polariz- 
ing action  of  such  currents. 

'Lapicque,  Compt.  raid.  soc.  bioL,  LXIII  (1907),  37. 


282    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

We  are  thus  led  to  consider  the  kinds  of  effect  which 
changes  in  the  electrical  polarization  across  the  cell 
surface  may  have  upon  chemical  processes  occurring  in 
this  region. 

It  should  first  be  noted  that  various  phenomena 
occurring  at  metallic  surfaces  and  involving  electrolysis 
have  been  shown  to  follow  the  same  '^ square  root  law" 
as  the  stimulation  process.  Bredig  and  Kerb  found  this 
to  be  true  for  the  influence  of  alternating  currents  in 
initiating  the  characteristic  rhythmical  action  in  the 
mercury  hydrogen  peroxide  system,  which,  as  we  have 
seen,  resembles  closely  the  passive  iron  model  in  its 
mode  of  activity;  the  same  was  found  by  Wilke  and 
Meyerhof  in  the  electrolytic  oxidation  and  reduction  of 
chromic  salts  and  chromates  at  platinum  electrodes.' 

Whenever  a  sufficient  uncompensated  potential 
difference  is  established  between  an  electrode  and  a 
solution,  as  in  any  battery  with  closed  circuit,  the 
conditions  for  chemical  change  are  present;  there  is  a 
transfer  of  electricity  associated  with  a  chemical  decom- 
position or  other  reaction  (oxidation,  synthesis,  etc.)  at 
the  interface.  It  is  well  known  that  a  certain  critical 
decomposition-voltage  must  be  exceeded  in  order  to 
carry  out  any  definite  electrolysis,  e.g.,  of  a  metallic 
salt;  and  if  the  cell  surface  possesses  the  general  proper- 
ties of  an  electrode,  the  chemical  reactions  there  occurring 
must  be  subject  to  similar  conditions.  The  need  for 
a  certain  minimal  or  ''threshold"  current-intensity  in 
stimulation  is  thus  explained ;  it  is  e\'ident  that  if  the  fore- 
going theory  of  transmission  is  wtU  founded  the  potential 

^  Bredig  and  Kerb,  loc.  cit.;  Wilke  and  Meyerhof,  Arch.  ges.  Physiol., 
CXXXVII  (1910),  I. 


STIMULATION  AND  TRi\NSMISSION  283 

difference  of  the  local  bioelectric  circuit  in  a  conducting 
tissue  like  a  nerve  must  exceed  the  critical  value  re- 
quired for  the  electrochemical  process  which  initiates  the 
chemical  reaction  of  stimulation.  The  general  nature  of 
the  conditions  will  be  considered  more  fully  later  when 
the  phenomena  of  transmission  are  discussed  in  detail. 
For  the  present  we  may  conclude  that  the  significance 
of  the  polarization  change  involved  in  electrical  stimula- 
tion is  simply  to  furnish  the  condition  required  for  some 
critical  chemical  decomposition  at  the  cell  surface. 
Presumably  this  chemical  change  alters  locally  the 
physical  properties  of  the  surface-film  in  such  a  way  as 
to  involve  local  breakdown  or  increase  of  permeability; 
and  then,  just  as  in  the  passive  iron  model,  an  auto- 
matically self-propagating  wave  of  chemical  decomposi- 
tion is  initiated.  In  this  process  the  altered  and  the 
unaltered  portions  of  the  cell  surface  act  as  two  electrode 
areas,  in  a  manner  analogous  to  that  obser\-ed  in  the 
passive  wire  and  similar  systems  during  transmission. 

In  living  tissues  the  conditions  are  more  complex 
than  in  the  sunple  model  considered  by  Xernst.  which 
takes  account  of  only  one  of  the  conditions  of  electrical 
stimulation.  Two  chief  conditions  which  this  simple 
theory  disregards  are:  (i)  the  existence  of  a  critical 
threshold  current-intensity,  indejK'ndent  of  duration; 
and  (2)  the  character  of  the  response  to  currents  of 
changing  intensity.  Nernst's  theory,  however,  ex])hiins 
the  essential  fact  of  polar  stimulation,  in  addition  to 
assigning  a  definite  condition,  viz.,  change  of  polarization, 
for  the  initiation  of  the  stimulation-process.  On  the  basis 
of  the  law  of  polar  stimulation  we  may  now  say  further 
that  a  change  of  polarization  in  a  defmite  dircclion,  such  as 


284   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

to  render  the  external  layer  of  the  solution  in  contact  with 
the  cell  surface  less  positive  than  before,  i.e.,  a  depolari- 
zation, is  the  critical  or  initiatory  event  in  stimulation.^ 
But  a  current  of  too  weak  intensity,  or  one  rising  to 
its  maximum  too  slowly,  will  not  stimulate,  whatever 
its  duration.  These  discrepancies  from  the  simple 
polarization  theory  must  be  referred  to  the  special 
properties  which  the  irritable  tissue  possesses  by  virtue 
of  being  a  living  structure.  Apparently  the  irritable 
element  is  able  to  compensate  slight  or  gradual  changes 
of  polarization  as  a  part  of  its  general  regulatory  capacity. 
Thus,  if  a  current  be  led  gradually  into  a  nerve  or  muscle, 
a  considerable  intensity  may  be  reached  without  stimula- 
tion. But  if  then  the  current  be  suddenly  broken, 
stimulation  results.  This  behavior  seems  to  imply 
that  while  the  current  is  gradually  increasing,  the  cell  by 
some  regulatory  process  maintains  its  normal  or  resting 
physiological  polarization  essentially  unaltered.  During 
the  flow  of  the  external  current,  part  of  the  polarization 
at  the  cell  surface  must  depend  on  the  presence  of  this 
current,  which  steadily  conveys  ions  to  (or  from)  the 
surface.  When  this  influence  is  suddenly  withdrawn, 
by  breaking  the  current,  the  effect  is  to  alter  the  polariza- 
tion more  rapidly  than  can  be  compensated  by  the 
activity  of  the  cell,  and  stimulation  results.  The  fact 
that  the  rate  of  change  to  which  the  irritable  element 
can  thus  adjust  itself  without  undergoing  stimulation  is 
rapid  for  rapidly  reacting  tissues  (i.e.,  those  with  brief 
chronaxie)  and  gradual  for  ''slow"  tissues  indicates  that 

»  Cf.  Briinings,  Arch.  ges.  Physiol,  C  (1903),  367.  Hermann  also 
recognized  that  the  polarization  change  of  stimulation  is  in  the  direction 
of  rendering  the  external  surface  of  the  irritable  element  less  positive 
than  before  (Joe.  cit.). 


STIMULATION  AND  TRANSMISSION  285 

some  specific  chemical  process,  whose  rate  is  determined 
by  the  characteristic  metabolic  properties  of  the  tissue, 
is  what  preserves  the  normal  resting  state  of  the  irritable 
elements.  Thus  we  may  imagine  the  material  of  the 
surface-film  as  being  constructed  and  replaced  as  rapidly 
as  it  is  removed  by  the  chemical  (reducing)  action  of  the 
current;  under  these  conditions  the  film  (with  its  resting 
polarization)  remains  unaltered  and  no  stimulation 
results.  But  if  the  rate  of  removal  exceeds  the  rate  of 
replacement,  the  consequence  is  alteration  of  the  film 
and  stimulation.  Conditions  of  essentially  this  kind 
exist  in  the  passive  iron  model,  which  shows  a  similar 
type  of  behavior. 

STIMULATION  BY  CONSTANT  CURRENTS 

A  typical  case  of  stimulation  by  the  constant  current 
will  illustrate  how  the  stimulating  effect  varies  with  the 
duration   of   the   stimulus.     The   following   table   from 


,0 


Temperature  ca.  15 

Sir/,;            i"'=-'y"->  'V> 

0.024 o.  18  279 

0.021 0.18  261 

0.017 o.  18  234 

0.014 0.18  212 

o.oi 0.2  200 

0.007 0.23  193 

0.0052 0.26  187 

0.0035 0.31  1S4 

0.0017 0.44  181 

0.00087 0.66  195 


Keith  Lucas'  gives  results  obtained  with  the  sartorius 
muscle  of  the  frog.     Constant  currents  of  known  intensity 

^J  Physiol.,  XXXVII  (1908),  475- 


286    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

were  passed  through  the  tissue  by  non-polarizable 
electrodes,  and  the  minimal  duration  required  for 
stimulation  was  determined  by  varying  the  distance 
between  two  contacts  (one  making,  the  other  breaking 
the  current)  in  a  swinging  pendulum. 

The  essential  feature  of  these  results  is  that  below 
a    certain    definite   intensity    of    current    (0.18    units), 
increasing  the  duration  has  no  effect  in  lessening  the 
intensity  required  to  stimulate;    i.e.,  weaker  currents 
will    not    stimulate,    whatever    their    duration.     This 
intensity  represents  the  critical  or  threshold  value  for 
any  current.     But  with  stronger  currents,  the  duration 
required  for  stimulation  becomes  less  as  the  intensity 
increases,  and  a  close  approximation  to  Nernst's  square 
root  law  is  found.     This  signifies  that  a  certain  minimal 
change  of  polarization  is  required  to  initiate  the  stimula- 
tion process;  with  currents  above  a  certain  critical  in- 
tensity this  polarization  is  attained  with  briefer  and  briefer 
durations   as   the   intensity   is  progressively  increased. 
Lapicque   and  other   observers   have   obtained   similar 
results.     The  current  of  threshold  value,  i.e.,  of  the  least 
intensity  that  will  stimulate  with  any  duration,  must 
traverse  the  tissue  for  a  certain  minimal  time  in  order  to 
stimulate.     This  time  is  characteristic  for  the  tissue  in 
question,  and  apparently  is  a  direct  function  of  the  rate  of 
certain  specific  metaboHc  processes;  probably  those  con- 
cerned in  the  alteration  of  the  surface-film,  as  indicated  by 
the  duration  and  other  features  of  the  refractory  period 
(see  below).     According  to  Keith  Lucas  and  Mines,  the 
length  of  this  minimal  time  varies  with  the  temperature 
of    the    tissue    in    accordance    with    a    somewhat    low 
temperature-coefficient,    similar    to    that    of    diffusion 


STIMULATION  AND  TRANSMISSION  287 

(Qio=i.3)-'  For  the  irritable  tissues  of  the  frog,  Lucas' 
gives  the  following  determinations  (at  ca.  13°):  sub- 
stance/3 (nerve  end-plate)  of  the  sartorius,  .001  second; 
motor  nerve-trunk,  .003  second;  muscle  liber  (sartorius), 
.02  second;  ventricle,  2  seconds;  for  smooth  muscle  the 
period  is  much  longer  (several  seconds).  Lapicque  finds 
the  least  effective  duration  of  the  minimal  stimulating 
current  to  vary  widely  for  the  muscles  of  ditTercnt 
animals,  and  gives  the  following  data:^ 

Muscle  Uast  Efftctive  nuni!ion 

ol  Threshold  Current 

Gastrocnemius  (rana  esculenta) 003  sec. 

Gastrocnemius  (r.  temporaria) 007  sec. 

Rectus  abdominis  (r.  esculenta) 009  sec. 

Gastrocnemius  (bufo  vulgaris) 013  sec. 

Foot  of  snail  (helix  pomatia) 048  sec. 

Foot  of  snail  (solen  marginatus) 075  sec. 

Ventricle  of  tortoise  (testudo  graeca) 082  sec. 

Claw  muscle  of  crab  (carcinus  mcenas) 30    sec. 

Mantle  muscle  of  mollusc  (aplysia  punctata) .  .   .80    sec. 

These  determinations  illustrate  the  specificity  of  this 
time-factor  for  different  animals.  It  is  interesting  to 
note  that  the  velocities  of  the  motor  ncr\T  imjnilscs  in 
different  animals  vary  in  a  closely  jxirallcl  manner. 
To  designate  this  characteristic  time-factor  in  the 
electrical  stimulation  of  different  irritaljle  systems, 
Lapicque  has  introduced  the  term  "chronaxie."  As 
now  defined,  the  term  has  reference  to  the  least  duration 
required  by  a  current  of  exactly  twice  the  threshold 
intensity  (or  so-called  ''rheobase"). 

» Lucas  and  Mines,  Journal  of  Physiology,  XXW'I  (1007),  334; 
Lucas,  ihid.,  XXXIX  (1910),  461;  cf.  p.  472. 

« Lucas,  Journal  of  Physiology,  XL  (1910),  225;  cf  p.  245. 
3  Lapicque,  Compt.  rend.  soc.  bioL,  L\'1I  (1905),  503. 


288    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

The  characteristic  time-factor  or  chronaxie  of  a  tissue 
also  expresses  itself  in  the  rate  of  variation  of  intensity 
required  by  the  stimulating  current;  this  rate  is  greater 
the  briefer  the  chronaxie;  it  is  also  greater  the  more 
rapidly  the  stimulation-process  develops  in  the  tissue, 
as  indicated  by  the  rate  at  which  the  accompanying 
bioelectric  variation  rises  to  its  maximum.  The  chron- 
axie also  varies  directly  with  the  duration  of  the 
summation-interval  for  subminimal  stimuU/ 

STEVIULATION  BY  CURRENTS  OF  CHANGING 

INTENSITY 

The  stimulating  effect  of  a  current  of  continuously 
changing  intensity,  or  of  a  change  in  the  intensity  of  a 
current  already  traversing  the  irritable  tissue,  varies, 
in  a  manner  which  is  characteristic  for  the  tissue,  with 
the  rate  of  change,  and  is  largely  independent  of  the 
actual  intensity.  It  is  significant  that  this  rule,  relating 
stimulating  effect  to  rate  of  change,  applies  also  to 
mechanical,  chemical,  and  other  forms  of  stimulation, 
in  all  of  which  a  sudden  change  is  more  effective  than  a 
gradual  one.  A  general  property  of  living  matter  is 
apparently  here  involved.  In  the  activation  of  the  fore- 
going metallic  model  (passive  iron  w^ire  in  nitric  acid) 
the  same  rule  holds;  e.g.,  in  order  to  activate  the  metal 
mechanically  by  scraping  with  glass,  the  movement 
must  be  rapid;  a  slow  movement  is  ineffective.  Similarly 
in  electric  activation  a  current  which  is  gradually 
increased  up  to  a  sufficient  intensity  has  no  effect, 
while  one  of  the  same  intensity,  attained  suddenly, 
causes  instant  activation. 

^  Cf.  Lucas,  Journal  of  Physiology,  XXXIX  (1910),  463;  cf.  p.  470. 


STIMULATION  AND  TRANSMISSION  289 

The  rate  of  change  which  a  current  requires  in  order 
to  stimulate  a  tissue  varies  with  the  nature  of  the  tissue, 
and  is  a  function  of  the  characteristic  chronaxie.  When 
the  chronaxie  is  brief,  the  rate  of  change  must  be  rapid. 
When  the  rate  of  change  of  an  increasing  current  is 
gradual,  a  greater  final  intensity  of  current  is  needed 
for  stimulation  than  when  this  rate  is  rapirj.  The 
following  observations  of  Lucas,  on  the  stimulation  of  the 
frog's  sartorius,  illustrate  the  conditions  for  a  single 
typical  tissue.  The  rate  of  change  of  the  exciting  current 
was  controlled  by  varying  the  rate  of  movement  of  a 
shutter  which  opened  and  closed  a  slot  in  a  partition  set 
across  a  zinc  sulphate  solution,  forming  ])art  of  the 
stimulating  circuit.^  Comparison  was  made  between  the 
current-strength  required:  (i)  when  the  circuit  was 
closed  instantaneously;  and  (2)  when  the  intensity 
was  increased  from  subminimal  to  a  stimulating  value 
at  varying  rates.  The  muscle  was  also  stimulated  by 
currents  of  the  same  linear  gradient  or  rate  of  change 
under  two  conditions,  (A)  while  immersed  in  pure 
0.7  per  cent  NaCl  solution  and  (B)  in  a  mixture  of  0.65 
per  cent  NaCl  plus  0.05  per  cent  CaCb.  The  following 
results  are  typical:^ 

Strength  of  Current  Required 
Time  Required  to  Reach  Full  for  Slimul.it ion 

Intensity  (Seconds)  ^  (NaCl)  B  (NaCl+C*Cl.) 

o  (instantaneous) ...  i  I 

o.  I  sec I  I 

0.27 1.05  1.07 

0.50 I.I  127 

0.97 i.iS  ^-5 

»  Lucas,  Journal  of  Physiology,  XXXVI  (1907),  253. 
^  Lucas,  ibid.,  XXXVII  (1908),  4591  cf.  p.  473- 


290   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

The  more  slowly  the  current  changes  its  intensity  the 
less  effective  it  is  as  a  stimulus.  The  sensitivity  to 
rate  of  change  varies  with  temperature  and  the  composi- 
tion of  the  medium;  the  necessary  rate  of  change  is 
greater  at  higher  temperatures;  it  is  also  greater  when 
calcium  is  present  (B)  than  in  the  pure  NaCl  solution 
(A).  According  to  Lucas,  "an  increase  in  the  concentra- 
tion of  the  calcium  would  appear  to  necessitate  a  more 
rapid  concentration  of  the  ions  concerned  in  excitation."^ 
Observations  by  Mines,  on  the  minimal  duration  of  the 
threshold  current  of  constant  intensity,^  have  shown 
that  in  this  case  also  the  duration  is  briefer  when  Ca 
is  present.  Such  facts  indicate  that  the  chronaxie  of  a 
tissue  is  determined  not  only  by  its  specific  constitution 
but  also  by  the  external  conditions  to  which  it  is  exposed. 
This  is  well  shown  in  certain  studies,  by  Adrian,  on  the 
effects  of  peripheral  nerve  injury.^ 

The  chronaxie  of  a  tissue  appears  to  be  closely 
related  both  to  the  rate  of  response  and  to  the  rate  of 
recovery  of  the  irritable  elements.  Thus  it  shows  a 
close  correlation  with  the  characteristic  duration  of  both 
the  bioelectric  variation  of  the  tissue  and  the  refractory 
period.  The  more  slowly  a  tissue  responds  to  a  constant 
current,  i.e.,  the  longer  the  minimal  duration  of  the 
current  of  threshold  intensity,  the  more  gradual  is  the 
rate  of  change  required  for  excitation  by  a  current  of 
changing   intensity.     The    length    of    the    summation- 

^  Op.  cit.  (1908),  p.  480. 

2  Cited  in  Lucas'  paper,  op.  cit.  (1908),  p.  472. 

3  The  chronaxie  of  a  muscle  with  nerve  supply  interrupted  increases 
progressively  until  innervation  is  re-established  {Archives  oj  Radiology 
and  Electrotherapy^  May,  19 17). 


STBIULATION  AND  TRANSMISSION  291 

interval   also  appears   to  be  determined   by   the  same 
conditions. 

SUMMATION 

The  phenomenon  of  summation  is  of  great  importance 
in  the  analysis  of  the  stimulation  process.  It  shows 
clearly  that  a  single  sul^minimal  stimulus  produces  an 
effect  on  the  tissue,  but  that  this  eiTect  is  transient; 
within  a  certain  brief  time  the  tissue  resumes  the  same 
condition  as  before  the  stimulus.  "But  if  before  this 
time  has  elapsed  a  second  similar  stimulus  is  apj)lied. 
its  effect  is  added  to  that  of  the  first,  and  the  critical 
level  of  disturbance  required  to  initiate  an  excitation- 
wave  may  be  reached.  The  second  stimulus,  in  order 
to  be  effective,  must  be  sent  in  before  the  etTect  of  the 
first  has  subsided;  and  the  more  rapid  the  rate  of  this 
subsidence  the  shorter  is  the  summation-interval.  The 
summation-interval  is  therefore  defined  as  the  longest 
interval  separating  the  successive  subminimal  stimuli 
of  an  effective  series  of  two  or  more  such  stimuli.' 

This  interval  is  shorter  than  the  least  duration  of  the 
exciting  current  of  threshold  intensity;  and  its  precise 
duration  varies  with  the  intensity  of  the  subminimal 
stimuli  employed.  Lucas  gives  the  following  intervals 
for  different  frog's  tissues  at  13°,  using  two  sui)minimal 
electric  stimuli  (induction  shocks)  which  were  5  per  cent 
below  the  strength  required  for  stimulation  by  single 
stimuli.^ 

Motor  nerve  (sciatic) 0004-.0005  sec. 

Muscle  (sartorius) 001 1-.0019  sec. 

Ventricle ooS  sec. 

^  Cf.  Lucas,  Journal  of  Physiology,  XXXIX  (1910),  46a. 
^  Op.  cit.  (19 10),  pp.  466  fl. 


292    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

When  the  shocks  were  lo  per  cent  below  the  threshold, 
the  interval  was  much  shorter. 

The  summation-interval  is  thus  longer  the  more 
gradual  the  excitation-process  (the  longer  the  chronaxie) 
of  the  tissue.  It  varies  with  temperature  and  with  the 
state  of  the  tissue.  Lucas  finds  the  temperature- 
coefhcient  to  be  low  (Qzo  =  ca.  1.3),  a  fact  suggesting  that 
purely  physical  changes,  e.g.,  diffusion-processes  (which 
have  a  similar  temperature-coefficient),  are  chiefly  con- 
cerned in  the  return  of  the  tissue  to  the  normal  after 
a  slight  disturbance.^  The  influence  of  the  inorganic 
salts  is  again  highly  interesting.  The  presence  of  Ca 
shortens  the  summation-interval,  just  as  it  shortens  the 
minimal  duration  of  the  threshold  constant  current  and 
increases  the  rate  of  change  required  for  stimulation  by  a 
changing  current.^ 

According  to  Lucas  and  Mines,  the  eft'ect  of  temper- 
ature on  the  minimal  duration  of  the  threshold  current 
is  the  same  as  on  the  summation-interval.  Such  facts 
again  emphasize  the  distinction  between  the  local  change 
produced  by  the  stimulating  agent  and  the  propagated 

^  Cf.  Lucas'  discussion,  op.  cit.,  p.  473.  It  is  noteworthy  that  the 
time  required  for  the  return  to  the  normal  properties  after  complete 
stimulation,  as  measured  by  the  length  of  the  refractory  period,  is  much 
longer  than  the  summation-interval,  and  that  the  temperature-coefficient 
of  this  return  or  recovery  process  is  high  (Qio  =  ca.  3) ;  these  facts  indicate 
that  chemical  processes  play  the  chief  part  in  the  recovery  from  a  com- 
plete stimulation.  The  ''local  change"  may  thus  be  of  a  purely  physical 
kind  (e.g.,  polarization  change),  while  in  the  complete  or  propagated 
excitation  the  chemical  factor  is  essential.  This  conclusion  agrees  with 
the  fact  that  the  refractory  period  is  much  longer  than  the  summation 
interval.  Apparently  the  former  represents  a  period  of  metabolic  and 
structural  restitution. 

*  Lucas,  op.  cit.,  p.  472. 


STIMULATION  AND  TRANSMISSION  293 

effect  or  stimulation-process  proper.  The  former  is. 
or  may  be,  a  purely  physical  change;  in  electrical 
stimulation  its  essential  feature  is  apparently  a  change  of 
polarization  resultini;  from  changes  of  ionic  concentration 
at  the  cell  surface.  This  change  does  not  initiate  a 
propagated  effect  unless  it  exceeds  a  certain  critical 
limit,  and  unless  the  state  of  the  tissue  is  favorable; 
thus  in  an  anaesthetized  tissue  the  local  change  of 
polarization  is  produced  by  a  current,  but  no  pr()i)agatecl 
excitation  follows.  The  differences  between  the  i)hysical 
conditions  and  manifestations  of  the  two  j)r()cesses, 
local  change  and  propagated  disturbance,  and  thi- 
differences  in  their  temperature-coefficients  show  that 
the  propagated  process  is  more  complex  than  the  initia- 
tory local  process  and  includes  chemical  or  metabolic 
factors  among  its  chief  components. 

GENERAL  NATURE  OF  STIMULATION  CHANGES 

The  factors  determining  the  characteristic  chronaxie 
of  a  tissue  would  thus  appear  to  be  largely  factors 
determining  the  rate  at  which  the  critical  j)olarizalion 
change  occurs  in  the  irritable  elements.  This  rate 
depends  on  the  rate  of  movement  of  ions  and  also  on  the 
special  structural  conditions  within  the  tissue.  An  impor- 
tant advance  in  the  theory  of  the  local  change  has  been 
made  by  Hill,'  who  has  modified  Xernst's  simj^lc  theor>' 
and  brought  it  into  closer  conformity  both  with  the 
facts  of  organic  structure  and  with  the  actual  behavior 
of  the  tissue  in  electrical  stimulation.  Hill  i)oints  out 
that  in  any  case  of  electrical  stimulation  ihc 
concentration-changes   at   tico   semi-permeal)le   surfaces 

» A.  V.  Hill,  Journal  of  Physiology,  XL  (1910),  190. 


294    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

situated  a  short  distance  apart  must  be  considered; 
these  are  the  surfaces  where  the  current-lines  intersect 
the  two  opposite  faces  of  the  irritable  element.  If 
these  surfaces  are  close  together,  the  diffusion-gradient 
set  up  by  a  given  current  is  steep,  and  hence  the  back- 
diffusion  opposing  the  polarization  is  relatively  rapid. 
The  production  of  the  critical  polarization  change  will 
then  require  a  stronger  current  than  with  the  membranes 
far  apart.  This  conception  explains  also  why  a  current 
passing  crosswise  through  a  nerve  or  parallel-fibered 
muscle  is  so  much  less  effective  than  one  passing  length- 
wise.    Hill's    calculation    leads    him    to    the    formula, 

i=    _   ^i,  for  the  conditions  of  stimulation  by  a  constant 

current,  w^here  X  is  a  direct  function  both  of  the  proximity 
of  the  two  membrane-surfaces  concerned  (proximity  being 
the  reciprocal  of  the  distance  apart)  and  of  the  rate  of 
movement  of  the  ions;  i  represents  the  intensity  of 
the  current,  /  its  duration,  and  /z  and  6  are  constants 
having  reference  to  the  conditions  of  movement  of  the 
ions  in  the  tissue.  This  formula  gives  a  remarkably 
close  agreement  with  observation  through  a  wide  range 
of  intensities.  A  further  essential  feature  of  Hill's  theory 
is  its  recognition  that  the  polarization  change  is  in  reality 
merely  the  determining  condition  of  a  chemical  change 
which  must  proceed  at  a  certain  minimal  rate  in  order 
to  cause  excitation.  From  this  point  of  view  it  is  possible 
to  understand  why  not  only  the  degree  of  polarization 
attained,  but  also  the  rate  at  which  this  critical  degree 
is  reached  determines  whether  stimulation  shall  be 
initiated  or  not.  The  stimulation  process  is  a  process 
sui  generis,  distinct  from  the  initiatory  physical  change; 


STIMULATION  AND  TRANSMISSION  295 

yet  it  is  of  such  a  nature  as  to  be  initiated  only  by 
physical  changes  proceeding  at  more  tlian  a  ccrlain 
rate. 

We  are  thus  led  again  to  consider  those  sj>ecial 
properties  of  the  living  system  which  it  possesses  by 
virtue  of  being  living;  i.e.,  metaboHcally  and  syn- 
thetically active.  The  features  above  of  stimuhition 
cannot  be  understood  except  by  reference  to  what  i.^ 
distinctive  in  vital  processes  as  such.  "S'ct  it  is  to  be 
noted  that  the  case  of  the  living  system  is  by  no  means 
unexampled  in  the  respect  just  considered.  There  are 
many  natural  processes  in  which,  if  a  certain  effect  is  to 
be  produced,  the  effecting  agent  must  act  at  more  than 
a  certain  minimal  rate;  if  it  acts  slowly,  the  elTect  fails 
entirely.  For  example,  a  swift  current  of  air  will  extin- 
guish a  candle  flame,  while  a  slow  one  will  not;  a  rapid 
stroke  will  ignite  a  match,  a  rapid  projectile  penetrates 
a  plate,  a  rapid  attack  succeeds  in  war  or  on  the  football 
field.  The  lighting  of  a  match  shows,  many  analogies 
with  stimulation.  Ignition  occurs  at  a  certain  critical 
temperature,  which  is  attained  when  the  match  head  is 
drawn  uniformly  over  a  rough  surface  for  a  certain 
time  at  more  than  a  certain  rate.  If  the  movement  is 
too  slow,  ignition  will  never  occur;  in  this  case  the 
stationary  condition  at  which  the  gain  of  heat  from 
friction  is  equal  to  that  lost  to  the  surroundings  by 
conduction  and  radiation  is  reached  at  a  temperature 
below  that  of  ignition.  A  mo\ement  at  a  certain  rale 
must  last  for  a  certain  time,  which  is  shorter  the  more 
rapid  the  rate.  Summation  phent)mena  and  summation 
intervals  may  also  readily  be  demonstrated  in  this 
system;    i.e.,   a  succession  of  brief  strokes  but  not  a 


296    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

single  stroke  will  ignite  if  the  interval  between  the 
strokes  is  not  too  long. 

It  will  be  evident  that  the  general  condition  common 
to  all  cases  of  this  kind  is  that  two  active  processes  or 
sets  of  processes,  with  resultants  acting  in  opposite 
directions,  are  concerned;  the  equilibria  are  ''dynamic" 
rather  than  static.  In  an  irritable  tissue  through  which 
a  uniform  electric  current  is  flowing,  the  effect  which  the 
current  produces  in  the  direction  of  stimulation  is 
presumably  counterbalanced  by  contrary  processes 
depending  largely  on  the  metabolic  or  synthetic  activity 
of  the  tissue.  Interruption  of  an  already  existing  uni- 
form current,  as  well  as  its  sudden  increase  or  decrease, 
disturbs  this  equilibrium  and  may  result  in  stimulation. 

Further  analysis  of  the  process  of  stimulation  requires, 
therefore,  a  consideration  of  the  special  nature  of  the 
processes  occurring  in  the  irritable  protoplasmic  system. 

According  to  the  foregoing  conception  of  the  condi- 
tions of  stimulation  in  living  cells,  the  primary  or 
initiatory  process  is  a  local  alteration  of  the  protoplasmic 
surface-film,  or  ''plasma  membrane,"  of  the  irritable 
element.  This  alteration  has  a  self-propagating  charac- 
ter, like  that  shown  by  other  chemically  alterable 
surface-films  at  the  boundary  between  two  electrically 
conducting  phases,  and  leads  secondarily  to  the  character- 
istic manifestation  of  cell-activity,  or  response.  If  this 
conception  of  the  stimulation  process  is  a  true  one,  all 
forms  of  stimulation  should  exhibit  definite  evidence 
of  accompanying  surface-processes  of  the  kind  indicated. 

Certain  effects  which  apparently  accompany  all 
forms  of  stimulation  and  activation,  whatever  the  special 
nature  of  the  response  may  be,  constitute  evidence  of 


STIMULATION  AND  TRANSMISSION  297 

this  kind.  These  are:  (i)  The  hioelectric  variations; 
(2)  the  presence  of  a  refractory  or  temporarily  incxcitable 
period  immediately  following  stimulation;  and  (3)  a 
temporary  loss  of  semi-permeability  or  increase  in  the 
permeabihty  of  the  cell  surface  to  water-soluble  sub- 
stances. 

We  have  seen  above  that  the  electric  cuirent  is  a 
universal  stimulating  agent;  and  that,  conversely,  when 
irritable  tissues  respond,  they  give  rise  to  electric  currents 
which  traverse  the  surroundings  and  may  be  there 
detected  by  appropriate  means.  Similarly,  mechanical  or 
chemical  alteration  of  the  cell  surface  causes  excitation 
and  also  gives  rise  to  bioelectric  currents.  Further,  during 
many  forms  of  normal  excitation  there  is  direct  evidence 
that  the  surface  layer  of  protoplasm  undergoes  a  sudden 
and  pronounced  change  in  its  properties,  one  effect  of 
which  is  to  increase  the  permeability  to  water-soluble 
substances;  in  many  cases  this  change  is  distinct  and 
easily  demonstrated;  e.g.,  the  turgor  mechanisms  of 
plants,  gland  cells,  and  egg  cells  during  activation;  in 
others  (nerve,  muscle)  the  indications  of  changing 
permeabihty  are  indirect.  The  loss  of  irritability  during 
the  refractory  period  is  also  in  harmony  with  the  hypotli- 
esis  that  the  surface  layer  breaks  down  or  is  othcnvise 
altered  during  stimulation,  since  semi-permeability, 
implying  electrical  polarizability,  is  apparently  essential 
for  stimulation;  any  temporary  loss  of  semi-i)ermeability 
must  therefore  involve  loss  of  irritability. 

The  strongest  evidence  that  the  surface-change  is  tlie 
essential  and  primary  change  in  stimulation  is  the  con- 
stancy with  which  the  foregoing  three  manifestations  of 
stimulation  are  associated.     Especially  signiiicant  also 


298    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

is  the  fact  that  closely  analogous  phenomena  are  observed 
in  the  inorganic  models  considered  above  (mercury- 
hydrogen  peroxide  catalysis,  passive  iron),  in  which  the 
process  of  activation  is  known  to  depend  upon  the 
electrolytic  disintegration  of  thin  interfacial  films.  In 
the  temporary  activation  of  passive  iron,  the  dissolution 
of  the  oxide-film  involves  (i)  a  change  of  potential,  (2) 
a  marked  increase  in  permeability,  allowing  ready  access 
of  the  acid  to  the  metal,  and  (3)  a  delay  in  the  recovery 
of  the  former  state  of  susceptibility  after  the  return 
of  passivity.  It  seems  highly  improbable  that  those 
parallels  are  accidental;  the  indications  are  that  they 
are  expressions  of  an  underlying  identity  in  the  essential 
structural  constitution  and  conditions  of  activity  of  the 
living  system  and  of  the  inorganic  model.  The  essential 
features  of  structure  and  composition  common  to  both 
systems  are,  briefly*  (i)  the  presence  in  both  cases  of  a 
thin  film  separating  two  electrically  conducting  phases, 
one  or  both  of  which  is  an  electrolyte  solution,  and  (2) 
the  susceptibility  of  the  film  to  alteration  under  the 
influence  of  electric  currents  (breakdown  or  construction 
by  local  electrolysis).  Before  dealing  in  greater  detail 
with  these  parallels  and  their  bearing  on  the  problem  of 
the  essential  constitution  of  living  matter,  it  will  be 
necessary  to  review  briefly  the  essential  facts  which 
have  been  established  with  regard  to  the  foregoing  three 
general  accompaniments  of  stimulation. 


CHAPTER  XIII 

BIOELECTRIC  PIIEXOMKXA 

A  complete  review  of  this  large  field  of  research  is  not 
possible  in  the  space  at  our  disposal.'  It  is  necessary, 
however,  to  consider  in  some  detail  the  chief  facts 
bearing  on  the  present  problem;  these  may  be  con- 
veniently grouped  under  the  two  headings:  (i)  bio- 
electric potentials  in  resting  cells  and  tissues;  and  (2) 
variations  of  bioelectric  potentials  in  relation  to  physi- 
ological activity. 

RESTING  BIOELECTRIC  POTENTIALS 

The  existence  of  potential-differences  between  the 
resting  cell  or  other  protoplasmic  element  and  its  sur- 
roundings has  in  itself  nothing  unexampled  or  surprising. 
Typically  such  potentials  are  found  at  all  phase- 
boundaries  unless  special  compensating  conditions  are 
present.  The  conditions  on  either  side  of  the  interface 
are  asymmetric  with  respect  to  chemical  composition 
and  physical  condition,  and  corresponding  to  this 
assymmetry  there  is  an  electrical  asymmetry  or  potential- 
difference.  The  facts  of  electrical  convection  and 
electrical  endosmose  show  the  presence  of  potential- 
differences  between  all  kinds  of  insoluble  mjjtcrials 
and  the  adjacent  layer  of  solution.     These  potentials 

^  For  an  exhaustive  account  of  the  earlier  work,  cf.  Bictlormann's 
Electrophysiologie,  English  translation.  For  a  more  recent  account, 
cf.  Bernstein's  Elcdrobiolflgic  (1912),  and  the  article  of  (iartcn,  "Trotiuk- 
tion  von  Elektrizitiit,"  in  Wintcrstein's  Handbuch  dcr  vcrgl.  Physiol., 
Ill  (1910),  105;  also  the  interesting  but  more  sj^ecial  work  of  Bosc, 
Comparative  Electro  physiology  (1907). 

299 


300   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

are  known  to  vary  with  the  composition  of  the  non- 
aqueous phase  and  with  the  electrolyte  content  of  the 
aqueous  phase;  i.e.,  ions  have  a  special  influence, 
although  surface-active  substances  other  than  electro- 
lytes may  also  have  an  effect,  as  already  shown.  The 
case  of  the  living  cell  falls  partly  in  this  general  category. 
Suspended  cells  travel  in  the  electric  field,  usually 
toward  the  anode;  and  the  rate  and  even  the  direction 
of  this  travel  may  be  changed,  just  as  in  non-living 
suspended  particles,  by  changing  the  electrolyte  content 
of  the  medium;  especially  active  in  this  regard  are 
H  ions  and  the  ions  of  polyvalent  metals.  Constant 
currents  passed  through  lii'ing  tissues  (muscle)  effect 
transport  of  fluid.  This  is  a  special  case  of  electrical 
endosmose;  evidently  any  passage  of  electricity  through 
a  cell  must  involve  some  displacement  or  transport 
of  fluid,  a  fact  which  must  be  considered  in  relation  to 
physiological  processes  like  secretion,  absorption,  and 
cell-division.  The  potentials  between  suspended  particles 
and  suspension-media  are  apparently  in  large  part  adsorp- 
tion potentials;  their  range  is  comparatively  narrow,  usu- 
ally between  0.02  and  0.05  volt;  according  to  Freundlich 
they  represent  the  potentials  between  an  adhering  im- 
mobile layer  of  solution  and  the  mobile  layer  adjoining.^ 
These  facts,  while  relevant  to  the  general  theory  of 
the  bioelectric  potentials,  do  not  in  themselves  explain 
sufficiently  the  special  peculiarities  of  the  latter.  Appar- 
ently the  closest  resemblances  are  with  electrode  poten- 
tials; e.g.,  those  between  a  metal  and  an  adjoining 
solution.     From  the  physiological  point  of  view  the  most 

^Freundlich,  Kapillarcheniie,  p.  243;  Report  on  the  Physics  and 
Chemistry  of  Colloids,  Faraday  Society  and  Physical  Society  of  London 
(London,  192 1),  p.  146. 


BIOELECTRIC  niEXO.MENA  301 

significant  fact  is  that  the  demarcation  potentials 
(shown  in  the  injury-currents  of  muscle  and  similar 
phenomena)  vary  with  the  condition  of  the  protoplasmic 
surface  layer.  The  loss  of  semi-permeability  accompany- 
ing death  is  always  associated  with  a  decline  or  dis- 
appearance of  the  demarcation  potential,  a  fact  indicating 
that  the  latter  depends  on  the  presence  of  a  semi- 
permeable partition  between  the  internal  protoplasm 
and  the  surrounding  medium.  Such  a  partition  allows 
the  existence  of  permanent  differences  of  electrolyte- 
content  between  the  solutions  adjoining  the  outer  and 
inner  faces  of  the  plasma  membrane,  and  so  provides 
the  asymmetric  conditions  necessary  for  a  potential- 
difference.  Just  why  this  potential-difference  should 
have  the  observed  orientation  (positive  externally)  and 
range  (of  the  order  of  0.05  to  o.i  volt)  is  not  entirely 
clear;  possibly  these  conditions  are  referable  to  a  higher 
total  electrolyte  content  of  the  cell  interior  as  compared 
with  the  surroundings,  or  to  a  preponderance  of  certain 
ions  (e.g.,  H  ions)  in  the  cell  interior.  The  chemical 
relations  between  the  ions  present  in  solution  and  the 
materials  composing  the  surface-film  are  undoubtedly  an 
important  factor,  and  it  seems  probable  that  oxidation- 
reduction  potentials  and  adsorption  potentials  (in  the 
Freundlich  sense)  are  also  concerned.  The  total  poten- 
tial as  observed  thus  represents  an  additive  effect. 

It  is  evident,  however,  that  the  demarcation  potential 
depends  primarily  on  the  special  physical  and  chemical 
properties  of  the  cell  surface,  since  whatever  modifies 
the  structure  or  chemical  character  of  the  j^rotoj^lasmic 
surface  layer  also  alters  the  potential.  This  is  shown  by 
the  conditions  under  which   the  so-called   currents  of 


302    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

injury  arise.  Mechanical  or  other  injury  and  the 
application  of  cytolytic  substances,  which  demonstrably 
increase  permeability,  always  lower  the  potential;  i.e.,  the 
altered  region  becomes  negative  relatively  to  unaltered 
regions.  This  effect  is  often  reversible  if  the  tissue  is  not 
exposed  too  long;  thus  potassium  salts  render  a  voluntary 
muscle  locally  negative,  in  accordance  with  their 
permeabihty-increasing  action;  and  if  the  tissue  is  soon 
afterward  bathed  in  Ringer's  solution,  the  original 
isoelectric  condition  returns.  Any  local  alteration  which 
impairs  semi-permeability  thus  induces  local  negativity; 
i.e.,  decreases  the  potential-difference  between  the 
protoplasm  and  the  surroundings.  The  fact  that  the 
variation  of  potential  is  always  in  a  negative  direction 
is  consistent  with  the  theory  that  the  normal  negative 
variation  accompanying  stimulation  is  also  the  effect 
of  an  alteration  of  the  cell  surface,  involving  a  temporary 
and  rapidly  reversed  increase  of  permeability.  We  may 
thus  understand  why  the  bioelectric  variation  of  stimula- 
tion is  similar  in  its  direction  and  range  to  that  accom- 
panying loss  of  semi-permeability,  while  differing  in 
being  reversible  or  evanescent. 

It  has  long  been  recognized  that  variations  in  the 
permeability  of  a  semi-permeable  partition  separating 
two  electrolyte  solutions  must  involve  variations  in  the 
potential  difference  across  the  partition,  and  the  chief 
modern  attempts  to  explain  the  bioelectric  potentials 
have  been  based  on  this  ground  (''membrane  theory" 
of  Ostwald,   1890,^  followed  by  Cybulsky,  Bernstein,^ 

^  Ostwald,  Z.  physik.  Chem.,  VI  (1890),  71. 

2  Cybulsky,  Bull.  Acad.  Sci.  de  Cracovie  (1898),  p.  231;  Bern- 
stein, Arch.  ges.  Physiol.,  XCIT  (1902),  521.  For  other  references  cf. 
Hober's  textbook,  op.  cit.,  p.  579. 


BIOELECTRIC  PHENOMENA  303 

and  others).  Ostwald's  original  suggestion  was  that 
the  plasma  membrane  may  act  as  an  ''ion  sieve," 
allowing  the  cations  of  some  intracellular  electrolyte 
to  pass  but  not  the  anions.  This  hypothesis  was 
adopted  by  Bernstein  as  affording  a  point  of  view  from 
which  the  sudden  fall  of  potential  during  stimulation 
might  be  explained;  at  this  time  Bernstein  supposed 
the  membrane  to  become  permeable  to  both  classes  of 
ions.  The  actual  conditions,  however,  are  undoubtedly 
more  complex,  and  include  other  factors  than  the  simple 
diffusion  potentials  considered  by  Ostwald  and  Bernstein. 
Nevertheless,  it  must  be  recognized  that  the  breakdown 
of  a  semi-permeable  partition  between  the  protoplasm 
and  its  medium  (the  two  adjoining  electrolyte  solutions 
concerned)  must  decrease  the  potential  between  the  two, 
whatever  the  detailed  conditions  of  this  potential  may 
be.  The  ''membrane  theory"  of  the  bioelectric  poten- 
tials need  not  necessarily  have  the  form  of  a  modified 
diffusion  theory,  as  some  of  its  opponents  seem  to  have 
supposed.  More  recent  developments  of  this  theory 
have  aimed  at  correlating  the  bioelectric  phenomena  with 
the  chemical  as  well  as  the  physical  processes  occurring 
in  the  protoplasmic  boundary  layers.  It  may  now  be 
taken  as  well  estabhshed  that  the  cell  surface  possesses 
electrode-like  properties,  and  that  in  the  determination 
of  its  electromotor  behavior  other  conditions  enter  than 
merely  a  selective  or  differential  hindrance  to  the  diflu- 
sion  of  ions. 

The  work  of  Macdonald'  is  of  special  interest  since 
it  first  showed  that  the  demarcation-potential  of  nerve 
varies  with  the  concentration  of  the  salts  in  the  adjoining 

^  Macdonald,  Proceedings  of  the  Royal  Society,  LXVII  (1900),  310. 


304   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

solution  in  the  same  manner  as  the  potential  difference 
between  a  metallic  electrode  and  its  adjoining  solution 
(e.g.,  Zn  in  ZnS04  solution).  When  the  demarcation 
potential  between  the  cut  surface  of  the  sciatic  nerve 
and  an  uninjured  area  one  centimeter  distant  was 
measured  (by  the  usual  compensation  arrangement), 
after  leaving  the  nerve  for  five  minutes  in  differently 
concentrated  solutions  of  a  given  salt,  results  of  the 
following  kind  were  obtained.  (The  potential  in  the 
original  physiological  salt  solution  is  represented  in  the 
bracketed  expression  by  E.) 

c«i.,f;^r.  Demarcation 

Solution  Potential 

m  KCL o.  lo  (=£  log  1.2) 

m/2 o .  34  ( =  £  log  2 . 2) 

m/4 , 0.6    ( =£  log  4) 

m/8 0.9    (  =  Elog  8) 

It  will  be  noted  that  the  potential  difference  increases 
with  increasing  dilution,  and  very  nearly  in  direct 
proportion  to  the  logarithm  of  the  dilution.  This  is  the 
characteristic  relation  found  in  electrode  potentials,  and 

expressed  by  Nernst  in  the  formula  E  =  RT  log  —  where 

C2 

Ci  represents  the  concentration  corresponding  to  zero 
potential  (equivalent  to  that  required  to  compensate  the 
ionic  solution-pressure  of  the  metal) ,  and  C2  the  concentra- 
tion of  the  ions  in  solution;  thus  with  zinc  in  contact 
with  ZnS04  solution,  the  potential  decreases  with  increase 
in  the  concentration  of  the  zinc  ions  in  a  logarithmic 
curve.  The  fact  that  a  similar  relation  is  found  with 
the  living  tissue,  and  that  the  results  obtained  are 
reversible,  as  Macdonald  found,  shows  that  the  living 
tissue  behaves  as  if  its  surface  were  an  electrode  reversible 


BIOELECTRIC  PHENOMENA  305 

with  respect  to  the  cations  of  the  solution.  Results 
similar  to  the  foregoing  were  obtained  also  with  XaCl  and 
HCL 

More  recently  Loeb  and  Beutner,'  in  an  extended  and 
important  series  of  researches,  have  shown  that  the 
characteristic  logarithmic  relation  between  the  concentra- 
tion of  the  ions  in  the  solution  and  the  potential  difference 
holds  for  organic  membranes  of  a  variety  of  kinds  and 
also  for  solutions  of  lipoids  in  organic  solvents.  The 
organic  membranes  act  as  if  they  were  reversible  to 
cations  as  a  class.  This  result  is  highly  significant,  for 
it  seems  to  imply  that  reversible  combinations  between 
these  ions  and  components  of  the  membrane  (e.g.,  pro- 
teins or  hpoids)  occur,  and  that  the  formation  of  these 
combinations  is  the  essential  factor  determining  the 
potential  equilibria  observed  in  a  given  solution.  Just  as 
a  metallic  electrode,  like  Zn  in  contact  with  a  solution  of 
ZnS04,  ^2,y  be  regarded  as  ''dissociating  off"  zinc  ions 
until  an  equihbrium  (to  which  corresponds  a  definite 
potential  difference)  exists  between  the  ions  tending  to 
pass  into  solution  from  the  metal  and  those  already  in 
solution,  so  in  the  case  of  a  salt  solution  in  contact 
with  an  organic  membrane  a  certain  potential  difference 
corresponds  to  the  equilibrium  existing  between  the 
ions  in  solution  and  the  ion-membrane  compounds 
formed  by  the  combination  of  these  ions  and  the  mem- 
brane components  (proteins,  etc.).  Any  increase  of  the 
ions  in  solution  decreases  the  potential  dilYerence  in 
logarithmic  ratio. 

»  Loeb  and  Beutner,  Science,  XXXIV  (191 1),  884;  XXXVII  (19 13), 
672;  Biochem.  Zeilschrift,  XLI  (1912),  i,  and  XLIV,  303;  LI  (1913),  288, 
301;  LIX  (1914),  195.     Cf.  also  Beutner,  ibid.,  XLVII  (1912),  73. 


3o6    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

The  demarcation  potentials  of  living  tissues  appear 
to  exemplify  this  general  condition.^  In  the  usual 
method  of  studying  these  potentials  in  muscle  or  nerve 
the  normal  cell  surface  in  part  of  the  tissue  is  first  altered 
by  mechanical  or  other  means.  The  electrodes  leading 
to  the  galvanometer  then  touch  two  surfaces,  altered 
and  normal,  which  differ  in  their  physico-chemical 
condition;  a  corresponding  potential  difference  is  shown, 
the  injured  region  being  negative.  Hence  the  term 
"alteration  current"  for  the  current  between  the  two 
regions.  Loeb  and  Beutner  found  the  same  to  be  true 
for  a  simple  organic  membrane  like  an  apple  skin; 
when  one  region  is  crushed,  this  region  shows  itself 
negative  to  an  unaltered  region;  potential  differences 
of  20  to  100  milH volts  were  observed  in  different  ex- 
periments, the  values  varying  with  the  concentration 
of  the  salt  solution  in  contact  with  the  tissue.^ 

Loeb  and  Beutner  found  also  that  the  potential 
changed  with  changes  in  the  concentration  of  the 
surrounding  solution  in  a  manner  similar  to  that  observed 
by  Macdonald  for  nerve.  To  produce  a  constant 
arithmetic  change  in  the  potential-difl'erence,  the  con- 
centration of  the  salt  had  to  be  changed  in  a  constant 
ratio;     i.e.,    to    a   geometric    series    of    concentrations 

^  The  importance  of  the  Donnan  membrane  potential  (potential 
across  a  membrane  permeable  to  only  a  part  of  the  ions  present),  in 
the  case  of  protein  solutions  separated  from  electrolyte  solutions  by 
collodion  or  similar  membranes,  has  recently  been  demonstrated  by 
Loeb  in  an  important  series  of  researches  (summarized  in  his  book, 
Proteins  and  the  Theory  of  Colloidal  Behavior).  In  this  case  a  colloidal 
ion  (protein)  is  the  one  to  which  the  membrane  is  impermeable.  In 
livdng  tissues,  however,  with  protein  ions  in  about  equal  concentration 
on  both  sides  of  the  membrane  (in  protoplasm  and  in  lymph)  this  source 
of  potential  can  scarcely  play  a  part. 

2  Biochem.  Zeitschrift,  XLI  (1912),  i;  cf.  p.  22. 


.  BIOELECTRIC  PHENOMENA  307 

corresponds  a  linear  series  of  potentials,  the  relation 
characteristic  of  electrode-potentials  in  general.  'J'hat 
the  effect  observed  in  any  single  case  depends  on  the 
special  character  of  the  surface  was  shown  in  a  series  of 
experiments  in  which  Loeb  and  Bcutner  compared  the 
effects  of  varying  the  concentration  of  the  s()luti(Mi  in 
contact  with  (A)  the  uninjured  surface  of  an  apple,  and 
(B)  a  surface  from  w^hich  the  skin  had  been  removed/ 
In  all  such  experiments  one  electrode  in  contact  with 
the  apple  remained  unchanged;  the  other  was  connected 
with  the  solution  which  was  varied;  the  latter  was  in 
contact  with  another  portion  of  the  surface  at  some 
distance  from  the  first  electrode.  A  quadrant  electrome- 
ter was  used. 

Potential  Difference  Observed  with  Solution  in  Contact 

Solution  A  (with  uninjured  skin)        B  (with  cut  surface) 

m/io,ooo  NaCl +0.175  +0.056 

m/iooo  NaCl +0.146  +0.036 

m/ioo  NaCl +0.086  +00.0 

m/io  NaCl +0.023  —0.022 

Both  surfaces  show  the  same  kind  of  variation  with 
varying  concentration  of  electrolyte,  but  the  altered  area 
shows  a  smaller  change  of  potential  for  a  given  change  of 
concentration;  thus  on  the  average  a  tenfold  dilution 
increases  the  positivity  of  the  unaltered  surface  by  about 
0.06  volt,  and  of  the  altered  by  about  0.03  volt.  With 
every  solution  used  the  altered  surface  exliibits  the  lower 
potential;  i.e.,  is  negative  relatively  to  the  unaltered; 
the  conditions  also  suggest  that  it  represents  an  area 
which  is  reversible   to  anions  as  well  as  to   cations,* 

^  Loc.  cit.,  1912. 

2  This  would  correspond   to  freer  penetration  by  anions  and  an 
entrance  of  diffusion  potentials  in  the  total  effect. 


3o8   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

while  with  the  intact  skin  the  reversibility  relates  to 

cations  alone.     In  other  words,  the  two  regions  exhibit 

different  electromotor  properties. 

Further  experiments'  showed  that  the  behavior  of 

the  organic  membrane  could  be  closely  imitated  by  an 

arrangement  in  which  a  solution  of  a   weak  organic 

acid  in  a  water-immiscible  solvent  is  in  contact  with  the 

salt  solutions.     In  the  arrangement  already  described : 

calomel      concentrated    membrane-  dilute            calomel 

electrode            salt              inclosed  salt            electrode 

solution           system  solution 

(e.g.,  apple) 

the  dilute  solution  is  positive  and  becomes  more  positive 

with  increasing  dilution;   such  a  chain  is  comparable  to 

one  containing  a  metal  in  contact  with  solutions  of  its 

salt;  e.g.: 

calomel      concentrated      metallic  dilute  calomel 

electrode         AgNOj  Ag  AgNOj         electrode 

in  which  also  the  side  containing  the  dilute  solution  is 
positive;  AgCl  may  be  substituted  for  metallic  silver 
with  the  same  result.     Similarly  the  arrangement : 


calomel 

concentrated 

solution  of 

dilute 

calomel 

electrode 

salt 

salicylic 

salt 

electrode 

solution 

acid  in 

salicylic 

aldehyde 

solution 

gave  potential  differences  of  a  similar  order  to  those 
found  with  the  organic  structure,  and  varying  similarly 
with  the  concentration  of  the  dilute  salt  solution.  In 
other  words,  the  surface  of  the  non-aqueous  phase  acts 

»Cf.  Beutner,  Trans.  Amer.  Electrochem.   Soc,  XXI  (1912),  219; 
XXIII  (1913),  401;  American  Journal  of  Physiology,  XXXI  (1913),  343- 


BIOELECTRIC  PHEXOMEXA  309 

in  the  same  manner  as  an  electrode  reversible  to  cations. 
The  remarkable  feature  is  that  the  reversibility  relates  to 
salts  of  cations  in  general,  and  not  only  to  those  of  a 
single  cation,  as  in  the  case  of  silver  or  other  metallic 
electrode.  All  of  the  alkali  and  alkali-earth  cations 
(those  of  the  chief  physiological  interest)  gave  typical 
results;  thus  with  KCl  the  following  obser\ations 
were  made;^  the  non-aqueous  phase  was  salicylic 
aldehyde  saturated  with  salicylic  acid: 

Concentration  E.M.F. 

of  KCl  Millivolts 

O.  1 6 

0.02 30 

0-004 55 

0.0008 89 

0.00016 130 

It  was  further  shown  that  this  effect  is  dependent  on 
the  acid  character  of  the  non-aqueous  phase;  i.e.,  on 
its  ability  to  take  up  cations  (reversibly)  by  salt  forma- 
tion; other  solutions  of  weak  acids,  e.g.,  of  benzoic  acid 
in  phenol,  behaved  similarly.  But  when  the  non- 
aqueous phase  is  basic  in  chemical  character,  the  potential 
changes  in  the  opposite  direction,  the  dilute  solution 
becoming  more  negative,  instead  of  more  positi\'e,  with 
increasing  dilution,  and  the  behavior  is  such  as  to  indicate 
reversibility  to  anions.  Beutner  found  this  to  be  the 
case  when  the  weakly  basic  compounds,  aniline  and 
toluidine,  were  used  as  the  water-insoluble  phase  in  an 
arrangement  similar  to  the  foregoing.^ 

^  Cf.  American  Journal  of  Physiology,  XXXI  (1913),  347- 

*  For  a  complete  account  of  Ikutncr's  investigations  cf.  his  recent 
book,  Entstehung  eleklrischer  Strome  in  kbcndcn  Gruebcn  (Stuttgart, 
1920). 


3IO    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

Such  facts  suggest  that  substances  having  the  proper- 
ties of  weak  acids  determine  the  type  of  electromotor 
behavior  shown  by  the  cell  surfaces  in  the  demarcation 
potentials.  Both  proteins  and  lipoids  (e.g., lecithin)  belong 
in  this  class.  Loeb  and  Beutner^  therefore  carried  out 
further  experiments  of  the  kind  described,  using  solutions 
of  lecithin  in  organic  solvents,  and  found  again  the  same 
relation  between  the  concentration  of  the  salt  and  the 
observed  potential  difference.  When  lo  per  cent  solu- 
tions of  lecithin  in  guaiacol  were  used,  the  behavior,  both 
quaHtative  and  quantitative,  was  found  closely  similar 
to  that  of  plant  tissues.  Oleic  and  palmitic  acids  gave 
similar  results,  but  not  cholesterol.  Extracts  of  various 
plant  and  animal  tissues  (muscle,  brain,  frogskin)  in 
organic  solvents  also  exhibited  this  behavior;  a  further 
interesting  fact  was  that  potassium  salts  had  a  greater 
influence  than  sodium  salts  in  altering  the  potentials, 
a  peculiarity  which  the  authors  ascribe  to  a  greater 
solubility  of  potassium  salts  in  the  lipoid  phase. 

It  would  seem,  therefore,  as  if  the  ordinary  potential 
differences  observed  between  altered  and  intact  portions 
of  the  cell  surface  were  phenomena  of  the  same  general 
type  as  those  just  described;  i.e.,  referable  to  the 
presence  of  a  water-insoluble  phase  containing  weakly 
acid  substances  and  forming  a  thin  film  or  partition 
between  two  dissimilar  electrolyte  solutions,  represented 
respectively  by  the  living  protoplasm  and  its  surrounding 
medium.* 

^  Biochem.  Zeitschrift,  LI  (1913),  288. 

» As  to  the  specific  nature  of  the  electrolytes  concerned,  little  definite 
can  be  said  at  present.  In  general  the  two  cations  whose  concentration  is 
higher  inside  than  outside  the  cell  are  K  and  H.     A  recent  calculation 


BIOELECTRIC  PHENOMENA  311 

VARIATIONS  OF  BIOELECTRIC  POTENTIALS 

The  sudden  fluctuations  of  potential  accompanying 
normal  vital  processes  like  stimulation  evidently  require 
a  different  type  of  explanation.  In  such  cases  rai)id  and 
reversible  alterations  of  the  electromotor  properties  of 
the  protoplasmic  surfaces  are  apparently  involved ;  these 
effects  can  only  be  referred  to  the  chemical  or  metabolic 
processes  characteristic  of  living  matter.  The  external 
surface  layer  of  the  living  cell  consists  of  a  thin  film  of 
chemically  alterable  material  in  immediate  contact  with 
the  surrounding  medium  on  the  one  side,  and  with  the 
internal  protoplasm  on  the  other;  it  is,  therefore,  subject 
not  only  to  purely  physical  changes,  such  as  local  thin- 
ning or  interruption,  but  also  to  changes  of  chemical  com- 
position, resulting  from  variations  in  oxidati\'e  or  other 
metabolism.  Along  with  such  alterations  must  go 
alterations  in  physical  properties,  thickness,  permeability 
to  electrolytes,  acid  or  basic  character,  etc.;  and  these 
must  alter  correspondingly  the  electromotor  properties 
of  the  cell  surface.  It  has  already  been  pointed  out 
that  the  reversible  variations  of  potential  seen  in  the 
action-currents  of  tissues  like  muscle  and  nerve  have  a 
range  closely  similar  to  that  of  the  demarcation-currents 
{ca.   0.05   volt);     and   this   fact   receives   a   consistent 


by  Adams  favors  the  idea  that  the  difference  between  the  internal  and 
external  H-ion  concentrations  is  an  important  factor  in  the  bioelectric 
potentials  {Journal  oj  Physical  Chemistry,  XXVI  [1922],  639). 

Recently  Rohonyi  has  opposed  Beutner's  conception  of  the  impor- 
tance of  an  oil-like  phase  in  the  determination  of  the  bioelectric  poten- 
tials; cf.  his  critique:  Biochcm.  Zcilschrift,  CXXX  (1922),  68.  He 
regards  semi-permeability  (permeability  to  water,  but  not  to  electrolytes) 
as  the  essential  property. 


312    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

explanation  on  the  li3rpothesis  that  dissolution'  and 
re-formation  of  the  semi-permeable  surface  layers  of  the 
cells  are  the  main  factors  in  the  production  of  the  normal 
electromotor  variations.  The  specifically  vital  functions 
of  metabolic  construction  and  destruction  which 
determine  the  physical  properties  of  the  cell  structures 
would  thus  determine  also  the  normal  variations  of  the 
bioelectric  potentials.  The  general  physico-chemical 
conditions  of  these  potentials  are  of  a  kind  present  at  all 
phase-boundaries;  but  the  special  peculiarities  of  the 
protoplasma  boundary  layers,  and  hence  of  the  dependent 
electromotor  phenomena,  are  determined  by  the  specific 
metabolic  activities  of  the  protoplasm  and  vary  with 
these  activities.  It  is  evident  that  metabolic  destruction 
and  re-formation  of  surface-films  would  involve  electromo- 
tor variations;  and  in  those  cases  where  the  film- 
material  is  susceptible  to  chemical  alteration  (e.g.,  oxida- 
tion or  reduction)  under  the  influence  of  the  local 
electric  currents  thus  arising,  the  conditions  would  also 
be  furnished  for  the  processes  of  spreading  and  trans- 
mission, which  are  essential  to  stimulation.  Conditions 
closely  resembling  in  their  general  features  those  just 
defined  are  in  fact  realized  in  the  passive  iron  model  and 
related  inorganic  systems  described  above. 

NORMAL  BIOELECTRIC  VARIATIONS  OR 
ACTION-CURRENTS 

The  present  view,  therefore,  refers  the  normal  bio- 
electric phenomena  to  variations  in  the  phase-boundary 

^  The  precise  nature  and  degree  of  this  alteration  are  unkno\\Ti;  the 
term  "dissolution"  may  be  regarded  as  indicating  an  alteration  sufficient 
to  deprive  the  surface  layer  temporarily  of  its  properties  as  a  membrane, 
i.e.,  as  a  semi-permeable  partition.  This  efifect  is  equivalent  to  increase 
of  permeability. 


BIOELECTRIC  PHENOMENA  313 

potentials  of  the  poly]:)hasic  living  system,  protoplasm, 
which  in  its  nature  is  subject  (especially  if  highly  "irrit- 
able") to  rapid  variations  of  chemical  or  metabolic 
activity.  Such  variations  imply  corresponding  altera- 
tions (breakdown,  construction,  etc.)  of  those  j)roto- 
plasmic  structures,  including  the  interfacial  films,  whose 
formation  and  maintenance  depend  on  this  metabolic 
activity.  Apparently  during  the  normal  stimuhition  of 
any  irritable  cell,  e.g.,  a  muscle  cell,  the  electromotor 
properties  of  the  cell  surface  change  in  such  a  manner 
that  the  surface  adopts  temporarily  properties  like  those 
of  an  injured  or  altered  surface;  i.e.,  one  which  has  lost 
its  semi-permeabiUty.  This  effect,  the  result  of  a 
metabolic  change  of  some  kind,  in  which  oxidations 
probably  play  a  chief  part,  is  a  reversible  one;  conse- 
quently a  reversible  electromotor  variation  accompanies 
it.  It  is  as  if  the  injury-current  were  temporary,  and 
lasted  for  only  a  brief  period,  whose  duration  depends  on 
the  rate  at  which  a  complete  surface  layer  with  the 
original  properties  can  be  re-formed.  It  has  already 
been  pointed  out  that  certain  forms  of  injury-current, 
those  caused  by  KCl  solution,  are  reversible  if  the  injury 
is  not  too  extensive.'  On  such  a  hypothesis  we  may 
understand  why  the  whole  reversible  bioelectric  variation 
occupies  a  definite  time,  characteristic  for  each  irritable 
tissue;  this  time  is  determined  by  the  tissue's  own 
specific  rate  of  metaboUc  construction  and  destruction. 
The    special    reaction-velocities    characteristic    of    the 

» It  is  well  known  that  with  excessive  stimulation  of  any  kind  the 
return  of  the  normal  positixity  is  delayed  or  incomplete  (Hermann  and 
others).  All  transitions  from  complete  reversibility  to  irreversibility 
can  be  obtained.  (Cf.  Ebbecke,  "Mcmbraniindcrung  u.  Xcrvcncr- 
regung,"  Arch.  ges.  Physiol.,  CXCV  [1922],  555;  cf.  pp.  581  fl.) 


314    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

particular  living  system  under  consideration  thus 
determine  the  duration  and  other  special  features  of 
its  action-currents,  and  hence  also  the  time-relations  of 
the  dependent  or  correlated  phenomena;  e.g.,  velocity 
of  transmission,  refractory  period,  summation,  and 
chronaxie. 

The  passive  iron  model  again  affords  a  clear  and 
simple  illustration  of  the  manner  in  which  rapid  electro- 
motor fluctuations  can  result  from  changes  in  the  char- 
acter of  the  boundary  layer  between  the  two  chemically 
interacting  phases.  When  such  a  wire,  immersed  in  a 
solution  of  nitric  acid  and  connected  through  a  voltmeter 
with  an  indifferent  electrode  (platinum  wire)  also 
immersed  in  the  acid,  is  activated,  a  sudden  change  of 
potential  (of  about  0.7  volt)  is  observed.  With  strong 
acid  (60  vols,  per  cent  1.42  acid  or  stronger)  this  variation 
is  automatically  and  rapidly  reversed  and  the  metal 
resumes  its  former  potential  within  a  second  or  two; 
this  reversal  is  a  result  of  the  re-deposition  of  the  passivating 
surface-film;  the  chemical  reaction  then  ceases.  Under 
certain  conditions  the  return  of  complete  passivity  may 
be  delayed,  or  rhythmical  fluctuations  of  potential  and 
chemical  activity  may  occur;  the  latter  phenomenon  is 
frequent  in  a  somewhat  weaker  acid  (between  50  and  55 
volumes  per  cent),  and  depends  upon  the  alternating 
formation  and  dissolution  of  the  passivating  film.^ 
Many  striking  electrical  phenomena,  having  features 
which  have  been  regarded  as  especially  characteristic 
of  bioelectric  processes,  are  in  fact  exhibited  by  this 
model.     These  phenomena  show  that  rapid  variations  of 

^  For  a  fuller  description  of  these  phenomena  cf.  my  article  in  Jour. 
Gen.  Physiol.  (1920),  op.  cit.,  pp.  1 13-15. 


BIOELECTRIC  niENOMENA  315 

potential,  with  associated  chemical  cfTects  fshown  in 
the  rapid  breakdown  and  replacement  of  tlie  surface- 
film  of  oxidation-product),  may  occur  in  a  three-phase 
system  of  relatively  simple  constitution,  when  the  third 
phase  has  the  form  of  a  thin  chemically  alterable  film 
between  the  other  two. 

In  a  chemically  reactive  and  film-partitioned  system 
such  as  living  protoplasm  processes  of  a  simihir  kind 
are  to  be  expected;  such  processes  would  here  also 
necessarily  be  associated  with  variations  of  potential. 
And  conversely,  since  in  all  processes  of  this  type  the 
factors  controlling  the  formation  and  breakdown  of  the 
hlms  are  mainly  electrical,  such  systems  would  be 
influenced  in  their  chemical  activity  by  electric  currents 
passing  through  them  from  external  sources.  This  is  in 
fact  true  both  for  metallic  systems  of  this  type  (which 
include  the  mercury-peroxide  system)  and  for  li\'ing 
protoplasm. 

In  living  organisms  variations  of  electrical  potential 
are  associated  with  physiological  activities  of  all  kinds; 
and  for  detailed  descriptions  of  the  bioelectric  phenomena 
and  for  a  review  of  the  extensive  literature  reference  must 
be  made  to  the  special  treatises  on  electrophysiology. 
Bioelectric  currents  have  been  shown  to  accompany  the 
following  vital  processes:'  automatic  or  reflex  activity 
of  the  central  nervous  system,  rhythmical  processes  like 
the  heartbeat  or  the  activity  of  automatic  nerve  cells, 
muscular  contraction,  nervous  and  other  forms  of  j)roto- 
plasmic  transmission,  glandular  secretion,  stimulation  of 
special  sense  receptors  (retinal  currents),  the  movements 

^  For  a  more  delailed  account  cf.  Garten's  article,  "Die  Produktion 
von  Elektrizitat,"  loc.  cit.,  1910. 


3i6    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

of  plants  (Mimosa,  Venus'  fly-trap),  and  growth  pro- 
cesses; they  are  probably  also  associated  with  cell- 
division  and  ciliary  movement. 

They  appear  in  fact  to  be  as  essential  a  feature  of 
protoplasmic  action  as  the  consumption  of  oxygen  or  the 
evolution  of  CO2.  The  fact  that  their  rate  of  develop- 
ment and  their  rhythm  are  influenced  by  changes  of 
temperature  in  the  manner  characteristic  of  chemical 
reactions  (Qio  =  2-3)^  indicates  their  dependence  upon 
the  fundamental  metabolic  processes  of  protoplasm. 
Direct  proof  that  the  bioelectric  rhythms  are  accompanied 
by  rhythmical  chemical  reactions  is  at  present  lacking, 
but  there  are  many  indications  that  this  is  the  case. 
The  evidence  is  clearest  in  those  instances  where  the 
rhythm  is  slow.  Thus  the  production  of  CO2  by  dividing 
sea-urchin  eggs  follows  a  rhythm  which  runs  parallel  with 
the  rhythm  of  cleavage;^  the  latter  rhythm  is  accom- 
panied by  a  parallel  rhythm  of  variation  in  the  physical 
properties  of  the  egg  surface;^  and  this  rhythm  is  almost 
certainly  associated  with  a  variation  of  potential."* 
In  a  certain  sense  it  is  self-evident  that  the  energy  of 
the  bioelectric  currents,  as  of  other  organic  activities, 
represents  the  transformed  energy  of  chemical  reactions; 

^  Cf .  Piper's  results  on  tortoise  muscle  {Elektro physiologic  mensch- 
licher  Muskeln,  Berlin  [191 1],  chap,  ix,  130).  Cf.  also  the  data  in  Gar- 
ten's article,  loc.  cit.;  also  Lucas,  Journal  of  Physiology,  XXXIX  (1909), 
207. 

'  E.  P.  Lyon,  American  Journal  of  Physiology,  XI  (1904),  52;  Science, 
XIX  (1904),  350. 

3  Cf .  my  paper  on  the  physiology  of  cell-division  in  the  Journal  of 
Experimental  Zoology,  XXI  (1916),  369. 

4  This  is  indicated  by  Miss  Hyde's  observations  in  the  Fundulus 
e^g,  American  Journal  of  Physiology,  XII  (1904),  241. 


BIOELECTRIC  rilENO.MENA  317 

but  the  problem  of  the  precise  nature  of  the  transforma- 
tion still  presents  many  difficulties. 

The  special  development  of  bioelectric  currents  as  a 
means  of  attack  and  defense  in  the  electric  fishes  is  a 
fortunate  circumstance  for  general  physiology,  since  the 
structural  conditions  found  in  the  electric  organs  are  full 
of  suggestion  for  the  general  theory  of  the  bioelectric 
processes.  These  conditions  indicate  clearly,  lirst,  that 
the  powerful  effects  produced  by  these  organs  depend  on 
the  summation  of  the  potentials  of  numerous  cellular 
elements  or  ''disks"  (apparently  modified  muscle  cells) 
arranged  in  series;  and,  second,  that  the  action  of  each 
single  element  depends  on  the  alteration  of  a  special  and 
definitely  oriented  portion  of  its  protoplasmic  surface 
layer.  This  area  is  structurally  characterized  by  the  rich 
branching  of  the  nerve-terminals  in  contact  with  it; 
it  forms  one  face  of  each  element,  posteriorly  directed 
in  the  case  of  the  electric  eel,  while  the  opposite  or 
anterior  face  is  free  from  nerve  fibers.^  One  face  of  each 
element  is  thus  innervated  and  apparently  undergoes 
alteration  or  activation  during  activity,  in  a  manner 
which  may  be  compared  with  that  of  an  activated  gland 
cell,  while  the  opposite  face  presumably  remains  un- 
changed. The  innervated  and  non-innervated  surface 
layers  of  adjacent  elements  thus  alternate  in  position  in 
a  manner  comparable  with  the  alternation  of  positive 
and  negative  metallic  plates  in  a  battery  of  galvanic  ele- 
ments in  series.  A  closer  comparison  would  be  with  the 
original  galvanic  ''pile,"  where  each  pair  of  plates,  copper 

»  Cf.  Gotch's  article  in  Schafer's  textbook,  II,  561,  for  an  account 
of   the   essential   structure   of   the   electric  organ;    also   Bicdcrmann's 

Electro  physiology  and  Bernstein's  Elcklrobiologic. 


3i8    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

and  zinc,  in  direct  contact  with  each  other,  is  separated 
from  the  next  pair  in  the  series  by  disks  of  cloth  or  paper 
soaked  with  electrolyte  solution.  Similarly  the  inner- 
vated and  non-innervated  surfaces  of  two  adjacent  ele- 
ments are  in  contact,  while  the  two  surfaces  of  the  same 
element  are  separated  by  the  mass  of  internal  protoplasm 
which  is  modified  in  a  characteristic  manner.  This  ar- 
rangement constitutes  strong  evidence  in  favor  of  the 
theory  that  the  surface-films  or  plasma  membranes  of 
these  cellular  elements  play  essentially  the  same  part  as 
the  electrodes  or  metallic  plates  in  batteries.'  In  the  ac- 
tive electric  organ  the  current  of  the  discharge  (positive 
stream)  runs  within  each  cell  or  element  from  the  inner- 
vated to  the  non-innervated  surface,  just  as  in  the  usual 
type  of  bioelectric  circuit  (e.g.,  of  a  single  muscle  cell)  the 
intracellular  direction  of  the  current  is  from  active  to  inac- 
tive (i.e.,  in  the  external  medium  from  inactive  or  ''posi- 
tive" to  active  or  "negative").  Although  the  E.M.F.  of 
each  cellular  element  is  small,  apparently  the  same  as  that 
of  a  single  muscle  cell  (viz.,  0.04-0.05  volt),  a  high  poten- 
tial between  the  terminals  of  the  series  is  attained  by 
means  of  the  summation  of  many  elements.  Briinings  has 
shown  that  by  arranging  several  frogs'  muscles  in  series, 
with  the  cut  surface  of  one  apposed  to  the  uninjured 
surface  of  the  next,  a  summation  of  potentials  may  be 
obtained.^  The  structure  of  the  electric  organ  is  thus 
in  striking  conformity  with  the  theory  that  the  bioelectric 
currents  originate  in  a  manner  essentially  similar  to  that 

'  Compare  Bernstein's  account  in  his  Elektrobiologie,  chap,  vi,  p.  121. 

2  Briinings,  Arch.  ges.  Physiol.,  XCVIII  (1903),  241.  According  to 
Briinings,  potentials  of  a  volt  or  more  can  be  obtained  by  arranging 
muscles  in  series. 


BIOELECTRIC  PHEN0:MEXA  319 

of  the  currents  produced  by  the  usual  combinations  of 
metallic  electrodes  and  electrolyte  solutions  (or  so-called 
''batteries"),  with  the  difference  that  in  the  living 
system  the  electromotor  surfaces  consist  of  thin  proto- 
plasmic films  having  a  composition  and  structure 
which  are  subject  to  rapid  variation. 

The  potential  changes  are  relatively  small  in  single 
cellular  elements  and  their  approximate  range  may  be 
readily  determined  in  parallel-fibered  muscles  like  the 
frog's  sartorius.  Here,  with  a  symmetrical  side-by-side 
arrangement  of  the  elements,  there  can  be  no  summation 
of  potentials;  and  the  conditions  are  like  those  of  a 
battery  arranged  ''in  parallel."  The  maximum  range 
of  variation  during  contraction  does  not  usually  appear 
to  exceed  0,05  volt,  a  potential-difference  similar  to 
that  of  the  demarcation-current.  According  to  some 
observers,  however,  the  potential  of  the  action-current 
in  muscle  during  strong  contraction  may  be  greater 
than  that  of  the  demarcation  current,  and  may  even 
attain  0.08  volt.  Comparative  observations  of  the 
demarcation-current  potentials  throughout  a  wide  range 
of  invertebrate  and  vertebrate  forms  give  magnitudes  of 
the  order  of  0.03  to  0.05  volt.'  The  exact  physico-chem- 
ical significance  of  these  values  cannot  be  stated  at  pres- 
ent. Bernstein  has  investigated  the  influence  of  temi)cr- 
ature  on  the  demarcation  potential  of  muscle,  and  finds 
that  within  the  physiological  range  (from  5°  to  30°),  its 
magnitude  is  closely  proportional  to  the  absolute  temper- 
ature, as  in  the  case  of  electrode  or  diffusion  potentials.' 

^  Cf.  the  data  in  Garten's  article,  loc.  cit. 

2  Bernstein,  Arch.  ges.  Physiol,  XCII  (1902),  521,  XXXI  (1910),  589; 
cf.  also  his  Elektrobiologie,  chap.  v. 


320   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

Considering  the  fact  that  the  potentials  as  measured 
must  be  less  than  those  actually  existing  in  the  living 
tissue — because  of  the  partial  cross-circuiting  of  the 
current  through  the  fluids  of  the  tissue — it  seems  probable 
that  in  typical  active  tissues  the  normal  fluctuations  of 
potential  in  single  cells  have  a  range  of  50  to  100  milli- 
volts. The  bioelectric  currents  are  thus  weak;  their 
intensity,  however,  is  amply  sufficient  to  excite  sensitive 
tissues,  as  is  demonstrated  in  the  laboratory  experi- 
ments in  which  nerves  and  muscles  are  excited  by 
demarcation  and  action  currents  (''rheoscopic  frog" 
experiments) . 

In  each  special  instance  the  duration,  the  rate  of  vari- 
ation, and  the  rhythm — in  the  cases  where  the  variations 
are  rhythmical — exhibit  special  features  characteristic  of 
the  tissue  and  of  the  species.  Comparison  of  the  condi- 
tions in  different  tissues  and  animals  reveals  the  exist- 
ence of  highly  significant  correlations  between  the  time- 
relations  of  the  electrical  response  and  of  the  normal 
functional  response  or  mode  of  activity  of  the  tissue. 
When  the  bioelectric  variation  develops  rapidly  and  is  of 
brief  duration,  the  response  of  the  tissue  to  stimulation  is 
also  rapid;  e.g.,  in  a  muscle  the  duration  of  the  latent 
period  and  of  the  single  twitch  is  brief,  the  chronaxie 
is  also  brief,  and  the  propagation  of  the  excitation-wave 
is  rapid;  the  refractory  period  and  the  summation- 
interval  are  also  brief.  On  the  other  hand,  tissues  with 
slowly  developing  bioelectric  variations  exhibit  a  slower 
rate  of  response  and  a  slower  subsidence  of  their  activity; 
the  muscular  twitch,  the  chronaxie,  the  refractory 
period,  and  the  summation-interval  are  relatively  pro- 
longed and  the  transmission  is  slow. 


BIOELECTRIC  PHENOMENA  321 

Changes  of  temperature  influence  the  functional 
processes  and  the  bioelectric  processes  similarly.  For 
example,  in  a  special  study  by  Keith  Lucas,'  in  which  the 
temperature-coefficient  of  the  rate  of  development  of 
the  bioelectric  variation  in  the  frog's  sartorius  was 
compared  with  that  of  the  propagation-velocity  of  the 
excitation-wave,  almost  identical  values  were  found  for 
the  two  processes.  In  a  typical  experiment,  the  time 
required  for  the  rise  of  the  bioelectric  variation  from 
zero  to  its  maximum  at  8°  was  .0041  of  a  second,  and  at 
18°,  .0024  of  a  second;  the  ratio  of  these  two  values, 
I  1.64,  was  almost  identical  with  that  of  the  propagation- 
velocities  of  the  excitation-wave  (contraction-wave)  at 
the  two  temperatures.  In  other  words,  change  of 
temperature  influences  the  rate  of  protoplasmic  transmis- 
sion in  the  same  manner  as  it  influences  the  rate  of 
variation  of  potential. 

It  seems  clear  that  the  bioelectric  variations  are 
inseparably  connected  with  chemical  or  metabolic 
processes  in  the  living  cells,  and  that  the  characteristic 
rate  at  which  the  tissue  reacts  and  conducts  excitation 
is  a  direct  function  of  the  rate  of  both  processes.  This 
rate  is  determined  by  the  specific  chemical  and  structural 
constitution  of  the  tissue  as  well  as  by  external  factors, 
such  as  temperature  and  the  state  of  the  surrounding 
medium.  The  evidence  already  reviewed  indicates  that 
the  essential  changes  underlying  the  bioelectric  phe- 
nomena occur  at  the  cell  boundary;  hence,  these  phe- 
nomena may  be  regarded  as  an  index  of  chemical 
decompositions  or  other  reactions  occurring  in  the 
protoplasmic  surface-films.     Apparently  these  reactions 

^Journal  of  Physiology,  XXXIX  (1909),  207. 


322    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

change  the  composition  of  the  films  and  alter  their 
electromotor  and  other  properties  (permeability,  physical 
consistency,  etc.),  and  the  bioelectric  currents  are  the 
result. 

The  question  of  whether  the  bioelectric  currents 
stand  in  the  relation  of  cause  or  of  effect  to  the  other 
physiological  activities  of  the  cell  is  not  one  to  be 
answered  simply,  since,  as  in  so  many  other  natural 
processes,  the  relations  are  of  a  reciprocal  kind.  Appar- 
ently the  conditions  are  of  the  same  general  physico- 
chemical  nature  as  in  any  reversible  type  of  galvanic 
cell  (storage  battery) ;  a  current  from  an  outside  source 
traversing  the  system  may  be  the  means  of  inducing 
definite  chemical  reactions  in  the  latter;  or  the  system 
may  by  its  own  spontaneous  chemical  action  generate  an 
electric  current  which  traverses  the  surroundings  and 
there  produces  the  usual  effects  of  such  currents.  Simi- 
larly, the  electric  variation  of  a  cell  or  nerve  fiber  may  be 
an  accompaniment  or  eft'ect  of  o.ther  processes,  pre- 
sumably chemical,  in  the  living  protoplasm;  but  once 
having  arisen,  a  bioelectric  current  may  act  in  the  same 
manner  as  any  other  electric  current  and  influence 
secondarily  other  processes  in  the  electrically  sensitive 
living  system.  Thus  there  is  every  evidence  that  the 
electric  factor,  as  such,  determines  the  transmission  of 
excitation  from  one  region  to  another  of  a  conducting 
nerve  fiber  or  other  excitable  protoplasmic  system;  and 
that  the  characteristic  rate  of  transmission  is  determined 
by  the  rate  at  which  the  local  variation  of  potential 
rises  from  zero  to  its  full  value. ^     It  is  evident  that  if 

'  Cf.  my  article  in  American  Journal  oj  Physiology,  XXXIV  (19 14), 
414. 


BIOELECTRIC  PHENOMENA  323 

each  active  region  excites  electrically  the  adjoining 
inactive  region,  by  means  of  the  local  bioelectric  current 
accompanying  activity,  the  velocity  with  which  excita- 
tion is  transmitted  from  region  to  region  will  be  higher 
the  more  rapidly  this  current  develops.  Lucas'  observa- 
tion just  cited  shows  in  fact  a  close  parallelism  between 
these  two  rates,  in  the  same  tissue  at  different  temper- 
atures. Variations  in  transmission-velocity  in  dilTerent 
tissues,  and  in  the  same  tissue  under  different  conditions, 
would  on  the  foregoing  hypothesis  have  a  direct  causal 
dependence  on  the  rate  of  change  of  potential  character- 
istic of  the  tissue. 

Reference  has  already  been  made  to  the  fact  that 
in  each  species  of  animal  the  bioelectric  variations  of 
the  active  tissues  have  specific  peculiarities — of  rate  of 
development,  normal  range,  duration,  rhythm,  etc. — 
which  exhibit  a  close  correspondence  with  the  peculiarities 
of  function  and  activity  characteristic  of  the  species. 
For  example,  the  normal  bioelectric  variation  of  a  special 
organ  like  the  heart  is  an  accurate  index  of  the  normal 
rate  and  sequence  of  its  difTerent  processes;  hence,  the 
electrocardiogram  may  be  a  delicate  means  of  detecting 
abnormalities  in  the  action  of  this  organ.  Presumably 
a  tracing  of  the  bioelectric  variations  from  the  group 
of  muscles  involved  in  the  act  of  speech  could,  with 
sufficient  knowledge  and  analytical  skill,  be  translated 
into  the  actual  words  uttered.  From  what  has  already 
been  said  it  will  be  obvious  that  this  close  correspondence 
between  the  functional  activity  of  a  living  system  and 
the  character  of  its  bioelectric  variations  implies  a  similar 
correspondence  of  both  with  the  underlying  variations 
of  metabolic  activity. 


324    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

The  range  of  the  electric  variations  obtained  from 
an  isolated  muscle  which  is  made  to  contract  in  a  graded 
manner  by  single  stimuli  of  different  strengths  shows 
a  direct  correlation  with  the  height  of  contraction,  but 
the  significance  of  this  fact  is  not  obvious.  It  is  pos- 
sible (i)  that  the  single  elements  or  cells  give  action- 
currents  of  varying  intensity,  or  (2)  that  each  element 
has  a  constant  variation,  but  that  the  number  of 
elements  excited  varies.  The  probabiHties  favor  the 
latter  alternative;  in  certain  tissues  such  as  heart 
muscle,  the  electric  variation  exhibits  a  constant  range 
which  is  independent  of  the  intensity  of  the  stimulus; 
the  whole  tissue  responds  with  a  complete  contraction 
to  any  sufhcient  stimulus — an  example  of  the  ''all  or 
none"  behavior — and  correspondingly  the  range  of  the 
electric  variation  is  constant.  There  is  good  evidence 
that  in  normal  unfatigued  voluntary  muscle  the  varia- 
tions in  the  strength  of  contraction  depend  on  the 
number  of  cells  contracting,  and  not  on  variations  in  the 
degree  of  contraction  of  single  cells. ^  Similar  considera- 
tions apply  to  the  bioelectric  response,  which  in  the  single 
elements  of  this  tissue  and  of  nerve  appears  also  to 
exhibit  the  "all  or  none"  character.  Apparently  to 
any  constant  manifestation  of  normal  physiological 
activity  a  constant  bioelectric  variation  corresponds. 

On  the  other  hand,  under  certain  abnormal  conditions 
the  bioelectric  variation,  e.g.,  in  heart  muscle,  may 
continue  without  the  normally  associated  contraction ;'' 

^  Cf.  Lucas,  Journal  of  Physiology,  XXX  (1905),  125;  XXXVIII 
(1909),  113;  F.  H.  Pratt,  American  Journal  oj  Physiology,  XLIV  (1917), 
517;  Pratt  and  Eisenberger,  ibid.,  XLIX  (1919),  i. 

^Noyons,  K.  Akad.  Wet.,  Amsterdam  (Nov.,  1908  and  April,  1910) 
(cited  in  Lucas'  Croonian  Lecture,  "The  Process  of  Excitation  in  Nerve 
and  Muscle,"  Proceedings  of  the  Royal  Society^  B,  LXXXV  [1912],  512). 


BIOELECTRIC  rHENO.MEXA  325 

in  such  cases  the  internal  contractile  mechanism  of  the 
cell  is  incapacitated;  and  apparently  this  may  occur 
without  disturbing  the  primary  processes  of  stimulation 
and  conduction,  which  depend  on  surface-changes 
associated  with  the  bioelectric  variation.  Such  a 
dissociation  of  conduction  and  excitation  from  contrac- 
tion is  also  seen  during  the  water-rigor  of  muscles;  at  a 
certain  stage  of  water-rigor  a  muscle  will  conduct 
excitation  without  contracting.^  Under  normal  condi- 
tions, however,  the  electromotor  variation  and  the 
functional  process  exhibit  close  parallelism.  The  inverse 
type  of  case,  i.e.,  where  a  muscle  contracts  or  nerve 
conducts  without  exhibiting  a  bioelectric  variation,  does 
not  seem  to  occur. ^  The  electromotor  variation  seems 
to  be  inseparable  from  the  process  of  stimulation.  It 
may  be  prevented  from  appearing  (by  anaesthesia,  etc.), 
but  in  that  case  all  of  the  other  manifestations  of  stimula- 
tion are  also  prevented.  Such  facts  again  indicate  the 
primary  and  controlling  role  of  the  electromotor  varia- 
tions in  cell-activities. 

TIME  RELATIONS  OF  BIOELECTRIC  VARIATIONS 

We  have  seen  that  the  time  occupied  by  a  single 
electromotor  variation  (i.e.,  of  the  unsummated  etlect 
resulting  from  a  single  stimulus)  varies  characteristically 

» Biedermann,  Sitziingsberichte  der  Akadcmie,  Wicn.,  XCVII  (1888), 
Part  III,  p.  loi;  cf.  also  Overton,  Arch.  ges.  Physiol.,  XCII  (1902),  146; 
he  finds  that  frog's  muscle  immersed  in  0.2  per  cent  NaCl  loses  con- 
tractility while  still  retaining  irritability  and  conductivity.  Cf.  also 
Hartl,  Engelmann's  Archiv  f.  Physiol.  (1904),  p.  80.  Robertson  has 
observed  the  same  phenomenon  in  the  intestine  of  the  Australian  blow- 
fly after  bathing  in  CaCh  solution  (Ergebnissc  dcr  Physiol,  X  I1910I,  305). 

»Cf.  Lucas'  discussion  of  this  question  in  his  Croonian  Lecture, 
op  cit,,  p.  502. 


326   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

from  tissue  to  tissue.  This  time  is  exceedingly  brief 
in  rapidly  responding  tissues  like  voluntary  muscle 
and  nerve;  for  example,  in  frog's  muscle  the  ''electrical 
response"  has  a  shorter  latent  period  and  a  much  shorter 
duration  than  the  ''mechanical  response";  the  muscular 
twitch  begins  (at  20°)  about  o.oi  of  a  second  after 
stimulation  and  lasts  about  o.i  second,  while  (according 
to  Snyder)  the  latency  of  the  electric  variation  is  about 
0.003  of  a  second  and  its  total  duration  about  0.007  of  a 
second.^  Thus  the  electric  variation  may  be  completed 
before  the  muscle  has  begun  to  contract;  it  is  the  first 
evident  effect  of  stimulation  and  apparently  is  an  index 
or  accompaniment  of  critical  changes  which  determine 
the  succeeding  chemical  and  mechanical  processes. 

In  general  the  more  rapidly  a  muscle  contracts  the 
briefer  is  its  chronaxie  and  the  more  rapidly  its  bioelectric 
variation  develops.^  There  is  also  a  direct  correlation 
between  the  rapidity  of  contraction  and  the  rapidity 
of  transmission  of  the  excitation-wave;  this  is  true  not 
only  for  the  transmission  in  the  muscle  itself,  but  also 
for  the  transmission  in  the  motor  nerve  supplying  the 
muscle. 3  Rapidity  in  physiological  action  thus  implies 
rapidity  in  the  associated  bioelectric  processes.  A 
muscle  and  its  motor  nerve  constitute  a  single  reaction- 
system,  and  the  rate  of  the  bioelectric  processes  is  a  close 
index  of  the  rate  of  reaction  of  the  entire  system.  Trans- 
mission of  the  excitation-state  from  nerve  to  muscle 
through  the  motor  end-plate  is  apparently  a  phenomenon 
of  the  same  kind  as  transmission  from  region  to  region 

^  a. CD. Snyder, American Joiirnalof  Physiology,'KXXlI(igi2) , ^:^6. 

^  Cf.  Lapicque,  Jour,  de  physiol.  et  de  path,  gen.,  X  (1908),  601. 

3  Carlson,  American  Journal  of  Physiology, 'K,  (1904),  401;  XV  (1906), 
136. 


BIOELECTRIC  riTENOMENA  327 

along  the  same  element.  Hence  if  transmission  is  a  case 
of  secondary  electric  stimulation  by  the  current  of  the 
local  circuit,  it  is  clear  that  rapidity  of  electromotor  varia- 
tion, implying  rapidity  of  conduction,  is  necessary  in  a 
nerve  which  excites  a  muscle  by  means  of  the  Ijioelectric 
circuit  formed  across  the  junction  between  nerve  fiber 
and  muscle  cell.  Lucas  has  furnished  evidence  that  the 
motor  end-plate  in  vertebrate  muscle  has  a  special 
chronaxie  differing  from  that  of  either  the  nerve  fiijcr 
or  the  muscle  cell,'  but  it  does  not  appear  that  the 
conditions  determining  the  transmission  between  nerve 
and  muscle  are  essentially  altered  by  the  presence  of 
this  intermediary  element.  According  to  Lapicque 
the  blocking  action  of  curare  results  from  an  alteration 
(slowing)  of  the  chronaxie  of  the  end-plate.^  Any  two 
contiguous  elements,  one  of  which  is  excited  by  the 
bioelectric  variation  of  the  other,  must  have  similar 
time-factors  of  excitation;  dissimilarity  in  the  time- 
factors  or  ''heterochronism"  (to  use  Lapicque's  term) 
would  be  inconsistent  with  such  transmission.  This 
conclusion  is  a  simple  corollary  of  the  general  laws 
of  electric  stimulation  described  above;  a  current 
traversing  an  irritable  element  must  have  more  than  a 
certain  duration  and  rate  of  change,  or  it  fails  to  stimu- 
late. Similarly,  the  momentary  current  at  the  myo- 
neural junction,  when  the  excitation-wave  traveling 
along  the  nerve  reaches  that  region,  must  have  a  duration 
and  rate  of  change  corresponding  with  the  chronaxie 
of  the  muscle  cell. 

» Lucas,  Journal  of  Physiology,  XXXVI  (1907),  113. 

2  Lapicque,  Compt.  rend.  soc.  bioL,  LXXII  (1913)1  674-     Cf.  how- 
ever, the  critique  by  Boruttau  in  Zcnlr.  Physiol. ,  XXXI  (1916),  303. 


328    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 


In  the  following  table^  are  collected  a  considerable 
number  of  observations  showing  the  rate  of  development 


Duration  of  Rising 

Phase  of  Action-Current 

Curve  {o-  =  .ooi  sec.) 


Tissue 

A.  Striated  Muscle: 

Frog's 
gastrocnemius. . .     2.58+3.84 


Frog's 

gastrocnemius. 
Frog's  sartorius .  . 
Frog's  sartorius .  , 
Frog's  sartorius .  , 
Frog's  sartorius . 
Frog's  sartorius .  , 
Frog's  hyglossus. 
Frog's  hyglossus. 

Mammalian  muscle 
Rabbit's 

gastrocnemius. . . 


{ca.  20°) 

1. 1-3. 5  {ca.  20°) 
1.6-3  2  {ca.  20°) 
4.1-4.2  (8°) 
2.4-2.9  (18°) 

13  (3°) 

5.8  (14.8°) 

20  (3°) 

8.9  (14-7°) 


ca.  2  {ca.  37°) 


B. 


Nerve  i^ 

Frog's  sciatic 0.9-1.2  {ca.  18°) 

Frog's  sciatic 0.55  (32°) 

Rabbit's  sciatic.  .  .  ca.  0.5  (32°) 

Dog's  sciatic ca.  0.7  (36°) 


Velocity  of  Propagation 
of  Excitation-Wave 


ca.  3-4  met.-sec. 

ca.  1.2  met.-sec.  (8°) 
ca.  1.65  met.-sec   (18°) 
1.06  met.-sec.  (3°) 
1.65  met.-sec.  (14.8°) 
0.38  met.-sec.  (3°) 
ca.  0.96  met.-sec. 
(14.7°) 


10-13  met.-sec.  in 
man's  forearm 

20-40  met.-sec.  at  20° 
30-80  met.-sec.  at  30° 
ca.  100  met.-sec.  at  37° 
ca.  100  met.-sec.  at  37° 


^  From  my  article,  American  Journal  of  Physiology  (1914),  loc.  cit.; 
the  observations  cited  are  from  many  different  authors;  for  complete 
references  cf.  this  article. 

2  These  observations  were  made  with  the  thread  galvanometer. 
More  recent  work  on  vertebrate  nerve  with  other  methods  indicates  that 
the  rise  is  even  more  rapid.  The  rates  shown  by  the  recent  work  of 
Gasser  and  Erlanger  with  the  cathode  ray  oscillograph  are  almost  double 
those  indicated  by  Garten's  observations  cited  in  the  table.  Cf. 
American  Journal  of  Physiology,  LXII  (1922),  517.  See  also  the  work 
of  R.  Plant  with  a  rheotome  method;  in  the  frog's  sciatic  the  rise  was 
estimated  at  0.2  to  0.30-  {Z.fiir  Biol.,  LXXVIII  [1923],  133). 


BIOELECTRIC  niEXOMEXA 


329 


Tissue 


Non-medullated 

(splenic  of  horse) 
Olfactory  of  pike  . . 


Duration  of  Rising 

Phase  of  Action-Current 

Curve  (<r  =  .ooi  sec.) 


ca.  60-70 
ca.  70  (12°) 


Commissural  of 
anodonta ca.  200 

Mantle-nerve  of 
octopus 8.2-1 1.3 

Mantle-nerve  of 
octopus ca.  20 

C.  Cardiac  Muscle: 
Ventricular  muscle 

of  mammal 10-15  (body 

temperature) 
Ventricular  of  frog .     40-60  {ca.  18°) 

D.  Smooth  Muscle: 
Retractor  penis  of 

dog ca.  2  sec. 

Ureter  muscle 0.2-0.4  sec. 

E.  Influence  of 
Narcotics: 

Frog's  sciatic Normal :     3  2-4 

(8.9°) 
Partly    narco- 
tized: 3.4-4.4 
Normal:  ca.  4,; 
narcotized . 
5.2-6 

Pike's  olfactory  .  . .     Normal:    55-60 

(ca.  9°);  partly 
narcotized: 
67-82 


Velocity  of  Pronaffation 
of  Kxcitation-Wavc 


ca.  0.47-0.54  met.-sec. 
60-90  mm. -sec.  (5°) 
1 18-150  mm. -sec.  (13°) 
160-240  mm. -sec.  (20") 

ca.  2.5  cm. -sec. 

(Varying     estimates 
from  I  to  5  cm. -sec.) 

2-5-3-5    met.    sec.    in 
O.  vulgaris 

ca.    2   met.-sec.    in   O. 
punctatus 


Averages      apparently 

2-4  met.-sec. 
From  50-200  mm. -sec. 


1-7  mm   sec;  average 

ca.  5  mm.-sec. 
Average  ca. 

14-15  mm.-sec. 


Average  17.3  met.-sec. 
in  normal;  ca.  12 
met.-sec  in  weakly, 
9.4  met.-sec.  in  more 
strongly  narcotized 
nervTS 

Average  normal  veloc- 
ity: ca.  81  mm.-sec; 
in  narcosis  ca.  50 
mm.-sec. 


330   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

of  the  local  bioelectric  variations,  as  related  to  the 
transmission-velocity  of  the  excitation-wave  in  a  variety 
of  vertebrate  and  invertebrate  tissues  under  different 
conditions.  It  will  be  noted  that  cold,  anaesthesia,  and 
fatigue,  which  retard  the  rise  of  the  bioelectric  variation, 
also  retard  the  speed  of  propagation  in  about  the  same 
proportion.  The  general  correspondence  shown  seems 
to  leave  no  doubt  that  a  direct  correlation  exists  between 
the  respective  rates  of  development  of  the  local  electric 
processes  and  the  velocities  with  which  excitation  is 
transmitted  from  region  to  region  in  the  different 
conducting  tissues. 

This  fact,  taken  by  itself,  may  seem  equivocal  in  its 
significance,  since  it  is  evident  that  any  wave  of  alteration 
occupying  a  definite  length  of  the  conducting  element 
and  associated  with  a  change  of  potential  would,  as  it 
passed  one  of  the  electrodes  of  a  recording  instrument 
(e.g.,  a  string  galvanometer),  cause  an  excursion,  the 
rate  and  duration  of  which  would  depend  on  the  speed 
of  the  wave.  The  electric  variation  might  thus  con- 
ceivably be  simply  a  sign  or  index  of  the  passage  of  a 
wave  of  activation,  without  having  any  causal  relation 
to  the  process  of  transmission.  Other  evidence,  however, 
to  be  considered  below,  indicates  that  the  electric 
variation,  as  such,  is  the  main  factor  determining  the 
transmission  of  excitation  from  the  active  region  to  the 
adjoining  resting  region  (see  chap.  xv). 

It  is  significant  that  many  normal  bioelectric 
processes,  e.g.,  those  accompanying  muscular  contraction 
or  nervous  activity,  as  they  occur  under  physiological 
conditions  in  the  intact  organism,  are  typically  rhythmi- 
cal.   The  underlying  chemical  reactions  must  therefore 


BIOELECTRIC  PHENOMENA  331 

also  be  rhythmical,  and  if  these  reactions  are  primarily 
those  occurring  in  the  protoplasmic  surface-films,  it 
follows  that  rhythmical  variations  in  metabolic  activity 
are  characteristic  of  this  region  of  the  cell.  There  are 
various  general  facts  indicating  a  tendency  to  rhythm 
in  the  activities  at  free  cell-surfaces;  for  example,  the 
wide  distribution  of  such  phenomena  as  ciliar>^  movement, 
in  which  protoplasmic  surface-processes  show  a  regular 
mechanical  rhythm  which  is  presumably  accompanied 
by  a  chemical  and  electromotor  rhythm.  The  filamen- 
tous processes  formed  under  certain  abnormal  conditions 
from  the  surface  of  simple  cells  like  blood  corpuscles 
also  often  exhibit  rhythmical  movements.^  All  such 
movements  are  probably  of  an  electro-capillarj^  nature, 
and  referable  to  general  conditions  similar  to  those 
determining  the  rhythmical  phenomena  in  the  j)olyphasic 
inorganic  systems  (mercury  in  hydrogen  peroxide,  iron  in 
nitric  acid)  described  above.  As  already  seen,  variations 
in  the  structure  and  composition  of  thin  interfacial  films 
are  the  essential  factors  in  all  such  phenomena. 

The  rhythmical  bioelectric  variations  accompanying 
the  normal  innervation  of  muscle  have  been  investigated 
in  much  detail  since  the  appUcation  of  the  thread 
galvanometer  to  physiological  uses  by  Einthovcii.  In 
man,  Piper  found  the  rhythmical  action-currents  obtained 
from  single  voluntary  muscles  (e.g.,  extensor  of  forearm) 
to  exhibit  a  remarkable  constancy  of  rhythm,  of  about 

^Cf.  Kite,  Journal  of  Infectious  Diseases,  XV  (1914)1  319;  Oliver, 
Science,  XL  (19 14),  645. 

The  minute  precipitation-filaments  first  fonncd  when  an  iron  wire 
is  placed  in  ferricyanide  solution  frequently  exhibit  rhythmical  move- 
ments of  a  kind  suggesting  ciliary  movement;  cf.  Biological  BuJUlin, 
XXXIII  (1917),  139- 


332    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

fifty  per  second.^  Records  taken  from  other  muscles 
showed  similar  but  not  always  identical  rates,  varying 
from  forty  per  second  in  the  thigh  muscles  to  sixty  per 
second  or  more  in  the  jaw  muscles;  and  it  appears 
probable  that  under  normal  conditions  different  muscles 
have  characteristic  differences  in  their  electromotor 
rhythms.  There  is  every  evidence  that  the  muscle 
rhythm  corresponds  to  the  electromotor  rhythm  of 
innervation,  which  in  turn  corresponds  to  the  rhythm 
of  discharge  from  the  nerve  cells  in  the  central  nervous 
system.  Numerous  observations  since  Helmholtz'  time 
have  shown  that  a  voluntary  muscle  during  contraction 
emits  a  low  musical  note,  apparently  indicating  a 
rhythmical  variation  in  mechanical  tension;  and  it  has 
been  shown  by  stimulating  the  nerve  rhythmically,  by 
tetanizing  currents  of  known  frequency,  that  the  note 
derived  from  the  muscle  has  a  pitch  corresponding  with 
the  rhythm  of  innervation,  up  to  a  frequency  of  several 
hundred  per  second.^*  The  same  is  true  of  the  rhythm 
of  the  electric  variation  obtained  from  the  muscle 
during  rhythmical  innervation;  in  the  frog's  muscle 
the  rhythmical  electromotor  variations  show  the  same 
frequency  as  that  of  the  stimulus,  until  an  upper  limit 
of  about  150  to  200  per  second  (at  room  temperature) 
is  reached;  above  this  limit  the  electric  variations  of  the 
muscle  are  less  frequent  than  those  of  the  nerve,  becoming 
irregular  with  the  higher  frequencies.^     In  the  case  of 

^H.  Piper,  Elektrophysiologie  menschlicher  Muskeln,  Berlin  (19 12); 
cf.  chap.  vii. 

2  Cf .  Piper,  op.  cit.,  chap,  x,  p.  143,  for  a  fuller  account  and  references 
to  literature. 

3  Cf.  F.  Buchanan,  Journal  of  Physiology,  XXVII  (1901),  95;  Hoff- 
mann, Archiv  Anat.  u.  Physiol.  (1909),  p.  43°;  also  Judin,  Arch.  ges. 
Physiol.,  CXCV  (1922),  527. 


BIOELECTRIC  PHEXOMEXA  ^^^ 

warm-blooded  animals  the  synchronism  between  inner\a- 
tion  and  the  electromotor  response  of  the  muscle  con- 
tinues up  to  frequencies  approaching  i,ooo  per  second.' 
Limits  are  set  to  the  possible  rate  of  electric  rhythm 
by  the  refractory  period  of  the  muscle  cells.  Recently 
Gasser  and  Newcomer,  using  an  amplifying  arrangement, 
have  shown  that  in  the  normal  innervaticjn  of  the  dog's 
diaphragm,  the  electromotor  rhythm  of  the  phrenic 
nerve  corresponds '  exactly  with  that  of  the  muscle; 
every  electromotor  wave  in  the  muscle  appears  to  be 
produced  by  a  corresponding  one  in  the  nerve;  the 
rhythms  observed  varied  between  72  and  104  per  second.' 
It  is  thus  clear  that  the  normal  rhythm  of  excitation  in 
the  muscle  cells  depends  on  the  rhythm  of  innervation; 
in  the  intact  organism  the  latter  rhythm  is  determined 
by  the  special  rate  of  rhythmical  discharge  characteristic 
of  the  motor  nerve  cells ;^  and  this  rhythm,  under  the 
usual  precisely  regulated  physiological  conditions,  is  re- 
markably regular. 

Experiments  of  Piper  on  the  influence  of  temperature 
on  the  natural  bioelectric  rhythm  in  the  tortoise-*  have 
shown  that  the  temperature-coefficient  of  the  rhythni 
is  of  the  usual  order  of  chemical  reaction-velocities. 
The  following  frequencies  of  oscillation  per  second  were 
observed  by  him  in  a  string  galvanometer  connected 
with  the  retractor  muscle  of  the  neck,  which  was  caused 
to  contract  reflexly  at  different  temperatures  (see  p.  334)- 

'  Cf.  Hober,  Arch.  ges.  Physiol,  CLXXVII  (1919),  305. 

'Gasser  and  Newcomer,  American  Journal  of  Physiology,  L\II 
(1921),  I. 

3  Cf.  C.  Foa,  Z.  alls.  Physiol.,  XIII  (191 1),  35- 

"Piper,  Arch.  Anal.  u.  Physiol  (Physiol.  Abthcil.)  (1910^  p.  ^07; 
also  Elektrophysiologic  menschliclicr  Muskcln,  cliap.  v,  p.  130. 


334   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

The  normal  tetanic  contractions  of  voluntary  muscles 
are  thus  summated  contractions  resulting  from  rhythmi- 
cal innervation.  We  can  thus  understand  why  the 
summated  contraction  resulting  from  artificial  rhythmical 
electrical  stimulation  of  the  muscle  is  physiologically 
indistinguishable  from  the  normal  contraction;  in 
reality  the  natural  as  well  as  the  artificial  tetanus  is  a 
result  of  rhythmical  electrical  stimulation.  Whether 
the  initial  electric  disturbance  in  the  muscle  cell  originates 

Temperature  Number  of  Waves 

7° 15 

12 19-20 

15-5 25 

18 29 

20 32-33 

22 35 

24 38 

26 40-41 

28 44 

30 47 

3^ SI 

34 54 

36 56 

at  the  motor  end-plate  or  at  the  point  of  entrance  of  a 
current  from  an  external  stimulating  electrode  is  a  matter 
of  indifference,  so  far  as  the  response  of  the  living  tissue 
is  concerned.  In  the  intact  organism  under  normal 
conditions  the  rate  of  rhythm  is  fixed  or  predetermined 
by  the  constitution  of  the  motor  cells  in  the  nervous 
system.  These  cells,  however,  are  subject  to  influence 
by  external  conditions,  such  as  temperature  or  the 
composition  of  the  surrounding  medium  (e.g.,  H-ion 
concentration),  so  that  many  physiological  rhythms  are 


BIOELECTRIC  PHENOxMENA  335 

subject  to  variation  in  frequency.  Such  \arialions  olTcr 
some  of  the  most  beautiful  examples  of  physiological 
adjustment  to  the  varying  needs  of  the  organism;  e.g.,  the 
respiratory  rhythm  of  warm-blooded  vertebrates. 

The  normal  rhythm  of  electromotor  discharge  may 
be  simple,  i.e.,  there  may  be  a  regular  succession  of 
single  impulses,  as  in  the  sinus  region  which  controls  the 
vertebrate  heart  beat;  in  this  case  both  the  unsummated 
character  of  the  muscular  contraction  and  the  form  of 
the  galvanometric  record  show  that  in  the  sinus,  auricle, 
or  ventricle  a  single  electromotor  variation  corresponds 
to  each  beat.  In  other  cases,  however,  a  rhythmical 
succession  of  discharges  may  occur,  each  discharge 
being  itself  rhythmical;  this  is  the  case,  for  exam])le, 
in  the  nerve  cells  innervating  the  respirator}^  muscles  of 
vertebrates.  Garrey  has  recently  observed  a  similar 
condition  in  the  Limulus  heart  ;^  corresponding  to  each 
beat  there  is  an  oscillatory  electrical  variation  or  dis- 
charge, undoubtedly  originating  in  the  ganglion,  each 
discharge  exhibiting  a  constant  number,  about  twelve, 
of  separate  electromotor  variations.  The  series  or 
''volley"  of  secondary  waves  or  pulses  forming  each 
discharge  has  its  own  rhythm,  which  is  independent  of 
the  cardiac  rhythm  as  a  whole.  Change  of  temperature 
changes  the  rate  of  oscillation  in  each  ganglionic  ''beat," 
but  the  number  of  distinguishable  oscillations  always 
remains  about  twelve.  It  appears  to  be  a  general  rule 
that  the  electromotor  rhythms  are  influenced  by  temper- 
ature in  the  same  manner  as  most  other  physiological 
rhythms,  i.e.,  show  the  chemical  temperature  coetTicient; 

^W.  E.  Garrey,  unpublished  observations  at  Marine  Biological 
Laboratory,  Woods  Hole,  Massachusetts. 


336   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

their  intimate  connection  with  the  metabolic  reactions 
of  the  living  protoplasm  is  thus  indicated. 

In  the  frog's  muscle  the  rhythmical  character  of  the 
bioelectric  current  during  tetanic  contraction  is  most 
readily  demonstrated  by  the  '^ secondary  tetanus" 
experiment,  in  which  a  muscle  with  its  nerve  laid  along 
another  muscle  is  thrown  into  tetanus  when  the  second 
muscle  is  tetanized.  In  man,  the  slight  mechanical 
oscillation  accompanying  steady  voluntary  contraction 
of  the  arm  muscles  can  be  demonstrated  by  means  of 
the  hot-wire  sphygmograph ;  this  mechanical  rhythm  has 
the  same  period  as  the  electromotor  rhythm;  i.e.,  about 
fifty  per  second.'  This  experiment  is  especially  interest- 
ing as  indicating  (as  do  also  the  experiments  with  the 
string  galvanometer)  that  the  various  nerve  cells  iner- 
vating  a  muscle  discharge  synchronously  or  in  phase  with 
one  another.  The  experiments  of  Gasser  and  Newcomer 
also  indicate  that  this  is  true  of  the  nerve  cells  innervating 
the  opposite  halves  of  the  mammahan  diaphragm.^ 
Apparently  the  several  nerve  cells  constituting  each 
motor  group  are  under  some  control  by  which  all  are 
impelled  to  react  synchronously,  or  ''keep  time."  This 
suggests  a  co-ordination  dependent  on  some  rapidly 
transmitted  influence,  presumably  electrical;  the  syn- 
chronous activity  of  spermatozoa  when  gathered  in 
clumps,  or  of  cihated  cells,  seems  to  be  a  phenomenon 
of  a  closely  related  kind  (see  p.  392). 

'A.  V.  Hill,  Journal  of  Physiology,  LV  (192 1),  Proceedings  of  the 
Physiological  Society,  p.  14. 

'  Gasser  and  Newcomer,  op.  ciL,  p.  24. 


CHAPTER  XIV 

MEMBRANE   CHANGES   DURING  STIMULATION 
REFRACTORY  PERIOD 

We  have  already  given  reasons  for  regarding  the 
bioelectric  variations  as  a  result  of  structural  change, 
controlled  by  metabolic  change,  in  the  protoplasmic 
surface  layers.  From  this  point  of  view  another 
constant  accompaniment  of  the  stimulation-process, 
the  refractory  period,  receives  a  consistent  theoretical 
explanation.  The  presence  of  the  intact  surface-film 
is  necessary  for  stimulation;  if  the  film  is  broken  down 
as  a  consequence  of  stimulation,  it  must  be  re-formed  and 
restored  to  its  original  state  before  a  second  complete 
stimulation  is  possible.  This  deduction  is  in  agreement 
with  our  general  experience  of  stimulation-processes. 
It  is  a  striking  fact  that  in  all  irritable  tissues  stimulation 
is  immediately  followed  by  a  period  of  inscnsitivity  and 
subnormal  irritability;  this  period  of  temporar)^  depres- 
sion, which  is  extremely  brief  in  rapidly  responding 
tissues,  is  the  refractory  period,  and  there  is  evidence 
that  it  corresponds  to  the  period  during  which  the  film 
is  undergoing  breakdown  and  reconstruction.  During 
the  refractory  period  the  tissue  loses  at  the  same  time 
both  its  susceptibility  to  electric  stimulation  and  its 
ability  to  transmit  states  of  excitation;  in  other  words, 
there  is  a  temporary  loss  of  both  irritability  and  conduc- 
tivity.^ 

»  Cf.  Lucas  and  Bramwell,  Journal  of  Physiology,  XLII  (191 1),  405; 
Adrian,  ibid.,  L  (19 16),  345. 

337 


338    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

The  duration  of  the  refractory  period  varies  greatly 
in  different  irritable  tissues,  and  under  normal  conditions 
is  specific  for  each  tissue.  The  most  significant  general 
correlation  is  that  it  is  brief  in  tissues  with  brief  chronaxie, 
and  vice  versa.  As  already  pointed  out,  in  any  irritable 
tissue  the  length  of  the  chronaxie  is  closely  related  to 
the  duration  of  the  single  bioelectric  variation;  and  the 
duration  of  the  refractory  period  shows  a  similar  correla- 
tion. This  parallelism  has  frequently  attracted  attention, 
and  its  significance  has  recently  been  discussed  in  con- 
siderable detail  by  Tait,^  who  has  reached  the  conclusion 
that  the  first  part  of  the  period,  the  interval  of  complete 
inexcitability  or  '^absolute  refractory  period,"  which  is 
of  brief  duration,  corresponds  with  the  period  of  upstroke 
of  the  curve  of  electromotor  variation,  while  the  ''rela- 
tive" part  of  the  period  corresponds  with  the  downs troke 
or  return  phase.  Tait  has  shown  that  the  relative 
refractory  period  is  greatly  prolonged  by  drugs 
(yohimbine,  protoveratrine)  which  retard  the  return 
phase  of  the  bioelectric  variation.  In  general,  he  finds 
the  return  of  irritability  to  run  parallel  with  the  return 
of  the  normal  resting  potential  of  the  muscle. 

While  it  seems  clear  that  the  delayed  recovery  in 
such  cases  has  a  connection  with  the  delay  in  the  recovery 
of  the  normal  electromotor  properties  of  the  tissue,  the 
correlation  is  apparently  not  a  simple  one.  More  recent 
evidence  shows  that  under  normal  conditions  the  relative 
refractory  period  in  muscle  and  nerve  may  last  several 
times  longer  than  the  return  phase  of  the  electric  varia- 
tion.^    The  curve  of  the  latter  is  very  nearly  symmetrical 

'  Tait,  Quarterly  Journal  of  Experimental  Physiology,  III  (191  o),  211. 

'  Cf.,  for  heart  muscle,  Trendelenburg,  Arch.  ges.  Physiol,  CXLIV 

(1912),  39;  for  nerve,  Adrian,  Journal  of  Physiology,  XL VIII  (1914),  453. 


MEMBRANE  CHANGES  DURING  STLMLXATION    339 

in  unfatigued  tissues,  while  the  change  in  irritability 
follows  a  markedly  asymmetric  course;  i.e.,  there  is  a 
rapid  and  complete  loss  of  irritability  on  stimulation, 
followed  by  a  relatively  gradual  recovery.  Evidently 
in  the  recovery  process  additional  factors  enter  which  are 
independent  of  the  bioelectric  variation.  It  is,  however, 
highly  signiticant  that  in  all  cases  irritability  seems  to 
disappear  completely  during  the  rising  phase  of  the 
variation.  This  partial  correlation  between  the  time- 
relations  of  the  two  phenomena  indicates  that  the 
conditions  determining  the  electromotor  variation  are 
closely  connected  with  those  determining  the  temporary 
loss  of  irritability. 

The  division  of  the  whole  refractory  period  into  two 
distinct  subperiods,  known  respectively  as  ''absolute" 
and  ''relative,"  is  its  most  interesting  feature.  The 
absolute  period  is  the  brief  interval  of  complete  insensi- 
tivity  immediately  following  a  single  eiTective  stimulus. 
During  this  interval  a  second  stimulus,  no  matter  how 
strong,  has  no  appreciable  effect.  It  is  as  if  the  tissue 
for  a  brief  time  lost  its  irritability  completely;  hence, 
two  stimuli  succeeding  each  other  within  tliis  interval 
produce  the  same  effect  as  a  single  stimulus;  while  if 
the  second  is  sent  in  after  the  completion  of  this  brief 
interval,  its  effect  is  seen  in  an  increased  resi)onse  or 
summation-effect.  The  completely  inexcitable  period 
in  a  frog's  motor  nerve  at  20°  lasts  about  0.00 1  to  0.0015 
of  a  second;'  in  the  sartorius  muscle  it  is  from  two  to 
three  times  longer;  and  in  both  of  these  cases  its  duration 
is  closely  similar  to  that  of  the  upstroke  of  the  bioelectric 

»  Cf.  Adrian,  Journal  of  Physiology,  XLVIII  (1914).  A^y,  L  (1Q16), 
345- 


340   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

variation.'  It  is  followed  by  a  second  period,  the  relative 
refractory  period,  during  which  irritability  returns 
progressively  to  normal;  this  interval  has  several  times 
the  duration  of  the  absolute  refractory  period,  and  in 
nerves  under  certain  conditions  (increased  H-ion  concen- 
tration) it  may  be  followed  by  a  brief  period  of  super- 
normal excitability.^  In  cardiac  muscle  the  return  of 
normal  excitability  is  relatively  very  slow,  even  when  the 
increased  duration  of  the  bioelectric  variation  is  taken 
into  account;  in  this  tissue  the  period  of  complete 
inexcitabihty  appears  to  outlast  the  entire  bioelectric 
variation,  and  its  limits  do  not  seem  to  be  very  clearly 
defined;  at  15°  Lucas  found  its  duration  to  be  somewhat 
more  than  0.4  of  a  second.^  Usually  it  has  been  supposed 
that  the  regular  and  somewhat  slow  rhythm  character- 
istic of  this  tissue  is  dependent  on  its  long  refractory 
period,  which  is  almost  equal  in  duration  to  the  period 
of  muscular  relaxation.  A  prolonged  refractory  period 
is  also  characteristic  of  the  nerve  cells  controlling  other 
physiological  rhythms  of  slow  period,  such  as  those  of 
certain  motor  reflexes  in  higher  vertebrates  (e.g.,  scratch 
reflex  in  the  dog). 

In  any  given  tissue  the  duration  of  the  refractory 
period  is  influenced  by  the  chemical  conditions  in  the 
surroundings  as  well  as  by  the  physiological  state  of  the 
tissue  and  the  temperature.     It  is  lengthened  by  fatigue, 

^  This  is  apparently  strictly  true  of  frogs'  voluntary  muscle,  but  in 
nerve  Adrian  finds  its  duration  somewhat  longer,  equal  to  that  of  the 
whole  bioelectric  variation.  In  cardiac  muscle  it  may  be  still  longer. 
Cf.  Adrian,  Journal  oj  Physiology,  LV  (1921),  193. 

2  Adrian,  Journal  oj  Physiology,  L  (1920),  i. 

3  Lucas,  Journal  of  Physiology,  XLI  (1910),  368;  cf.  pp.  383-84. 


MEMBRANE  CHANGES  DURING  STLMl'LATIOX    341 

lack  of  oxygen,  and  partial  ana'sthcsia,  at  least  in  some 
cases;'  but  in  nerve  Lucas  found  the  rate  uf  rccoverv 
to  be  normal  in  solutions  of  alcohol  sufficient  to  p^reatly 
retard  transmission.^  Bazett  observed  an  inlluencc  of 
the  salts  of  the  medium,  increase  of  potassium  lengthen- 
ing, and  increase  of  calcium  shortening  the  interval.-* 
Various  poisons  such  as  veratrine,  muscarine,  digitalis, 
and  barium  salts  also  lengthen  the  refractory  period.'* 

The  temperature-coefficient  appears  to  be  high  in  all 
cases.  In  frog's  muscle  and  nerve  Bazett  and  Adrian 
obtained  Qio  values  of  three  or  more.^  Burdon-Sanderson's 
observations  on  the  frog's  heart  indicate  values  ranging 
from  2  to  2.5.^  The  fact  that  the  process  of  recovery 
shows  this  high  coefficient  seems  to  indicate  its  depend- 
ence upon  processes  of  constructive  metabolism:  the 
temperature-coefficients  are  in  fact  similar  to  those  of 
growth  processes. 

It  is  interesting  to  note  that  the  various  forms  of 
protoplasmic  transmission  (in  nerve,  muscle,  etc.), 
which  theoretically  depend  on  processes  of  breakdown, 
have  usually  shown  temperature-coefficients  of  a  tlis- 

^Cf.  Verworn,  AUg.  Physiol.,  4th  ed.,  Jena  (1903),  p.  559; 
Irritability,  Yale  University  Press,  1913,  chap,  xii;  FrOhlich,  Z.  allg. 
Physiol.,  Ill  (1904),  468. 

'Journal  of  Physiology,  XL  VI  (i9i3)>  470- 

3  Bazett,  Journal  of  Physiology,  XXXVI  (1908),  414. 

4  Cf.  Tait,  loc.  cil.;  Trendelenburg,  loc.  cit.;  dc  Boor,  Jourtuil  of 
Physiology,  XLIX  (1915),  312;  American  Journal  of  Physiology,  XLVII 
(1921),  179,  189. 

5  Cf.  Bazett,  loc.  cit.;  Adrian  (1914),  and  (192  0,  loc.  cit. 

6  Eckstein  {Arch.  ges.  Physiol,  CLXXXIII  [1920],  40)  finds  a 
value  of  2.6  for  the  refractory  period  of  frogs'  ventricle  (average  of  10 
experiments  between  5°  and  20°). 


342    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

tinctly  lower  order  (Qio=  1.5-2).'  The  significance  of 
this  fact  is  not  altogether  clear,  but  it  suggests  that  purely 
physical  factors  play  more  part  in  the  destruction  than 
in  the  reconstruction  of  the  surface-film.  There  are 
general  reasons  for  expecting  that  a  process  of  structural 
breakdown,  in  which  purely  physical  factors  predominate, 
will  have  a  low  temperature  coefficient;  accordingly, 
since  protoplasmic  transmission  is  apparently  dependent 
on  such  a  breakdown,  it  is  not  surprising  that  its 
temperature-coefficient  should  be  lower  than  that  of  the 
recovery  process,  which  presumably  is  chiefly  a  result 
of  metaboHc  reconstruction.  Let  us  suppose  that  the 
first  stage  in  the  local  excitation-process  consists  in  a 
removal  or  destruction,  by  chemical  reaction,  of  those 
constituents  of  the  plasma  membrane  which  are  respon- 
sible for  its  semi-permeabihty  and  coherence;  and  that 
the  second  stage,  immediately  following,  is  some  purely 
physical  process  of  disintegration  or  falling  apart,  in 
which  diffusion-processes  are  the  chief  factor.  Then  the 
chemical  temperature-coefficient  will  be  shown  by  the 
first  stage  only,  while  the  second  and  probably  longer 
stage  will  have  the  coefficient  of  dift'usion-processes. 
The  whole  process  will  then  have  a  low  temperature- 
coefficient  similar  to  that  observed,  as  the  following 
simple  calculation  shows. 

We  assume  that  the  total  period  of  breakdown  at 
20°  has  a  duration  of  3  cr  (about  the  duration  of  the  rising 

I  For  the  temperature  coefi&cient  of  the  nerve  impulse  cf.  Maxwell, 
Journal  of  Biological  Chemistry,  III  (1907),  359;  Snyder,  American 
Journal  of  Physiology,  XXII  (1908),  179;  Harvey,  Carnegie  Institute 
Publications,  CXXXII  (1910),  35;  Lucas,  Journal  of  Physiology, 
XXXVII  (1908),  112.  For  the  transmission  of  the  contraction  wave 
muscle  cf.  Woolley,  Journal  of  Physiology,  XXXVII  (1908),  122; 
Lucas,  ibid.,  XXXIX  (1909),  207. 


MEMBRANE  CHANGES  DURING  STIMn, A'lION   343 

phase  of  the  bioelectric  variation  in  frog's  voluntary 
muscle),  and  that  of  this  period  one-third  (i  a)  is  occupied 
by  the  initial  chemical  decomposition  (C«,.).  ^vith 
Qio  =  3y  and  the  remaining  two-thirds  (2(7)  by  a  physical 
disintegration  (P^oO,  with  Qio=i.3  (the  tempcrature- 
coefhcient  of  diffusion  processes).  Then:  (i)  Total 
duration  of  breakdown  at  20°,  C2o»+P2o''  =  3  ^1  (2)  total 
duration  of  breakdown  at  10°,  Cio»+Pio°=i  (rX3-f  2  <tX 

1.3  =  5.60-.  The  ratio  - —  ,  is  1.9,  the  Q,o  for  the  total 

process. 

This  value  is  similar  to  those  obtained  by  a  number 
of  investigators  (Maxwell,  Lucas,  Woolley,  Snyder,  and 
Harvey)'  for  the  transmission-process  in  nerve  and 
muscle.  The  recovery -process,  on  the  other  hand, 
which  apparently  occupies  the  greater  part  of  the 
refractory  period,  presumably  depends  chietly  upon  the 
reconstruction  of  the  surface-film  by  metabolic  synthesis, 
and  accordingly  exhibits  the  high  temperature-coethcient 
characteristic  of  chemical  processes. 

The  general  theory  of  the  refractory  period  is  thus 
closely  related  to  that  of  the  stimulation-process  as  a 
whole.  If  stimulation  is  in  fact  dependent  on  an  al- 
ternate breakdown  and  reconstruction  of  the  surface- 
films  of  the  irritable  elements,  we  should  expect  irritabiHty 
(which  depends  on  the  state  of  the  film)  to  var>'  during 
the  successive  stages  of  the  stimulation-process  in  a 
manner  very  similar  to  that  which  we  observe. 
Evidently  there  are  two  distinct  processes  involved  in 
the  local  change  of  stimulation,  corresponding  rcsjicc- 
tively  to  the  ''absolute"  and  the  "relative"  periods.    The 

'  Loc.  c'U 


344   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

view  has  long  been  entertained  (by  Hering  and  others) 
that  the  rising  phase  of  the  bioelectric  variation  is 
coincident  with  a  period  of  breakdown  of  living  material, 
and  the  return  phase  with  its  reconstruction.^  In 
Tait's  experiments  just  described,  the  delay  in  the 
return  phase  of  the  variation  was  found  to  be  associated 
with  a  delay  in  the  recovery  of  normal  irritability  and 
conductivity;  hence  his  proposal  to  identify  the  relative 
refractory  period  with  the  period  of  recovery  or  recon- 
struction of  which  the  return  bioelectric  variation  is  the 
index.  There  are,  however,  various  facts  indicating 
that  the  return  variation  and  the  recovery  of  irritability 
may  vary  independently.  Trendelenburg  has  shown 
that  in  cardiac  muscle  excitability  does  not  return 
until  some  time  after  the  bioelectric  variation  is  com- 
pleted; poisoning  with  muscarin  lengthens  the  refractory 
period  without  greatly  affecting  the  bioelectric  variation.^ 
From  general  considerations  a  complete  coincidence  is 
hardly  to  be  expected.  Although  the  existence  of  a 
certain  normal  bioelectric  potential  between  protoplasm 
and  medium,  the  so-called  '^ physiological  polarization," 
is  apparently  necessary  for  stimulation,  it  is  known  that 
a  tissue  may  be  rendered  inexcitable  by  conditions 
that  have  little  effect  on  this  potential,  e.g.,  the  presence 
of  anaesthetics,  Mg  salts,  etc.  It  is  probable  that  the 
normal  physiological  polarization  is  regained  rapidly 
during  the  early  part  of  the  refractory  period,  as  shown 
by  the  completion  of  the  return  variation  of  potential; 
this  change  apparently  indicates  the  return  of  the  altered 

^  Cf.  Hering,  "Theory  of  the  Functions  in  Living  Matter,"  Brain, 
XXII  (1897),  232  (translation  of  article  in  Lotos,  IX,  Prague  [1888]). 

2  Cf.  Trendelenburg,  loc.  cit.;  also  the  discussion  in  Adrian's  paper, 
loc.  cit.  (192 1). 


MEMBRANE  CHANGES  DURING  STIMULATION    345 

surface-film  to  its  previous  continucjus  and  semi- 
permeable state;  yet  the  film  may  require  some  further 
structural  or  chemical  modification  before  it  is  in  a 
condition  favorable  for  stimulation  and  transmissi(3n. 
The  relative  refractory  period  seems  to  correspond  to 
the  time  during  which  those  regulatory  or  restorative 
changes  are  proceeding  in  the  newly  re-formed  film. 

These  general  considerations  receive  support  of  an 
indirect  kind  from  my  recent  experiments  on  transmission 
and  recovery  of  transmissivity  in  passive  iron  wires 
immersed  in  nitric  acid  solution.'  In  tliis  inorganic 
model  there  is  also  a  refractory  or  non-transmissive 
period  immediately  following  the  passage  of  an  activation- 
wave.  During  the  progress  of  the  chemical  reaction 
following  the  activation  of  a  passive  wire  in  60  per  cent 
HNO3,  the  metal  exhibits  the  chemical  and  electrical 
properties  of  ordinary  or  active  iron,  and  is  insusceptible 
to  further  activation.  This  initial  period  of  activity 
may  be  compared  with  the  absolute  refractory  period 
in  the  living  tissue.  Its  onset  is  accompanied  by  a 
variation  of  potential,  the  active  metal  becoming  negative 
(anodal)  relatively  to  its  previous  condition  by  cii.  0.7 
volt.  After  a  brief  interval  of  vigorous  chemical  reaction, 
lasting  from  one  to  two  seconds,  the  metal  reverts 
spontaneously  to  the  passive  state,  the  cfi"crvesccnce 
ceases,  and  the  potential  immediately  becomes  again 
positive.  During  the  first  minute  or  so  after  this 
automatic  repassivation  it  is  found  impossible  to  reactiv- 
ate the  metal  completely  by  local  mechanical  or  chemical 
treatment;  e.g.,  touching  the  wire  with  zinc  produces  a 
brief  and  partial  activation  which   is   transmitted   for 

^Jour.  Gen.  Physiol.,  Ill  (1920),  107,  129. 


346   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

only  a  short  distance;  by  degrees  transmissivity  returns, 
and  in  one-and-a-half  or  two  minutes  (at  20°)  is  as 
complete  as  before.  In  this  case  the  return  of  passivity 
— ^with  the  potential  characteristic  of  that  state — depends 
on  the  re-deposition  of  a  thin  surface-film  of  oxidation- 
product.  This  process  is  itself  a  rapid  one,  as  shown 
by  the  rapid  change  of  potential  from  negative  to  positive; 
but  the  metal  is  at  first  relatively  resistant  to  alteration, 
and  regains  its  former  properties  only  by  degrees, 
probably  as  a  result  of  a  progressive  thinning,  rearrange- 
ment of  molecules,  or  other  change  in  the  film,  accom- 
panying the  approach  to  the  equihbrium  condition. 
If  we  may  regard  the  processes  in  the  inorganic  model  as 
resembling  in  their  general  features  those  of  the  irritable 
Kving  system,  it  would  seem  probable  that  in  the  latter 
the  ''absolute"  refractory  period  represents  the  early 
phase  in  the  local  stimulation-process  during  which  the 
alteration  and  breakdown  of  the  protoplasmic  surface- 
film  are  in  progress;  while  the  ''relative"  period  is 
that  during  which  the  film  is  being  rebuilt  and  reconsti- 
tuted in  the  succeeding  recovery-process.  As  the  film 
returns  toward  the  normal  or  equihbrium  condition,  the 
ability  of  the  tissue  to  respond  and  transmit  excitation 
also  returns.  It  is  interesting  to  note  that  the 
temperature-coefficient  of  the  process  of  recovery  in 
passive  iron  is  high  and  apparently  similar  to  that  of 
living  tissues  (Qio  =  2-3).^ 

PERMEABILITY-INCREASE  AND  STIMULATION 

If  during  the  local  stimulation-process  there  is  in 
fact    a    temporary   breakdown    or   dissolution    of    the 

^  Ibid.,  p.  126 


MEMBRANE  CHANGES  DURING  STLMULAllUN    347 

protoplasmic  surface-film,  a  temporary  increase  of 
permeability  to  water-soluble  diffusible  substances  should 
be  associated  with  stimulation.  The  nurnial  semi- 
permeability  of  the  living  cell,  implying  impermeability 
to  water-soluble  substances  of  low  molecular  wcij^ht 
(neutral  salts,  sugars,  and  amino-acids),  depends  on 
the  structural  continuity  of  the  plasma  membrane;  and 
when  this  continuity  is  interrupted  in  any  way,  the  effect 
is  equivalent  to  a  loss  of  semi-permeability.  Such  an 
effect  may  be  temporary  and  difficult  to  detect  in  those 
cases  where  the  surface-film  is  rapidly  re-formed;  but 
in  the  more  favorable  instances  we  should  ex])ect  to  lind 
direct  evidence  of  increased  permeability  during  stimula- 
tion, in  addition  to  the  indirect  indications  afforded  by 
the  bioelectric  variation  and  the  refractory  period. 

According  to  the  present  theory,  the  local  electric 
effects  upon  which  the  transmission  essential  to  stimula- 
tion depends  are  the  result  of  local  alterations  of  the 
cell  surface,  involving  increased  permeability.  Con- 
versely, therefore,  we  should  expect  permeability- 
increasing  agents  as  a  class  to  cause  stimulation  of 
irritable  cells.  The  production  of  an  ''injury-current" 
by  mechanical  or  other  means  shows  that  local  interrup- 
tion in  the  physical  continuity  of  the  cell  surface  forms 
a  local  circuit;  and  the  formation  of  this  circuit  may  be 
the  means  of  starting  a  propagated  disturbance  or 
wave  of  excitation,  in  the  same  manner  as  a  local  inter- 
ruption in  the  surface-film  of  the  passive  iron  wire  starts 
a  wave  of  activation.  It  is  well  known  that  the  ai)plica- 
tion  of  a  cytolytic,  i.e.,  permeability-increasing,  substance 
to  a  living  tissue  produces  a  local  electrical  negativity, 
giving  rise  to  an  injury-current,  and  that  this  current  is 


348    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

sufficiently  strong  to  excite  other  irritable  tissues. 
Hence  the  local  production  of  such  a  current  within  the 
irritable  element  itself  might  be  expected  to  cause 
stimulation  in  adjoining  area^  of  the  same  element, 
an  effect  which  would  be  repeated  at  the  boundary  of 
each  area  thus  secondarily  stimulated,  and  thus  form 
the  condition  for  a  spread  of  excitation,  in  the  manner 
already  indicated. 

There  is,  in  fact,  a  large  body  of  evidence  indicating 
that  any  rapid  local  increase  of  permeability,  however 
induced,  acts  as  excitant  to  an  irritable  cell  or  element. 
Mechanical  treatment,  like  pricking  or  sudden  pressure, 
the  sudden  application  of  heat,  and  rapidly  acting 
cytolytic  agents  all  have  a  stimulating  effect  on  muscle 
or  nerve.  It  is  interesting  to  note  that  many  cells,  not 
ordinarily  classed  as  irritable,  undergo  rapid  and  spon- 
taneous structural  alteration  or  breakdown  under  condi- 
tions involving  local  increase  of  permeability.  This  is 
well  seen  in  the  effects  following  the  puncture  with 
capillary  needles  of  the  surface  of  red  blood  corpuscles 
and  other  cells;  frequently  a  disintegration  starts  at 
the  point  of  injury  and  rapidly  leads  to  the  breakdown 
of  the  entire  cell.^  In  a  red  corpuscle  thus  treated  the 
exit  of  haemoglobin  may  be  seen  to  begin  simultaneously 
over  the  whole  surface.^  It  is  clear  that  in  such  cases 
the  surface-film  undergoes  a  sudden  and  irreversible 
increase  of  permeability;  this  change  is  propagated  over 
the  whole  surface,  and  apparently  in  many  cases  through- 

^  Cf .  Kite,  American  Journal  of  Physiol.,  XXXII  (1913),  146; 
Chambers,  Science,  XL  (1914),  824;  XLI  (1915),  290;  Oliver,  Science, 
XL  (1914),  645. 

2  Cf.  Chambers,  Anatomical  Record,  X  (19 16),  190. 


MEMBRANE  CHANGES  DURING  STLMULATION    349 

out  the  internal  protoplasm  as  well,  with  the  result  that 
the  cell  breaks  down.  The  rapid  disintegrations  charac- 
teristic of  the  ''explosive"  blood  corpuscles  of  Crustacea^ 
and  of  the  vertebrate  platelets,  and  the  phenomena 
exhibited  by  other  rapidly  and  irreversibly  reacting 
cells  like  nematocysts  and  certain  unicellular  gland 
cells,  appear  to  be  examples  of  the  same  type  of  process. 
In  all  such  cases  the  surface-film  is  stable  only  so  long 
as  its  continuity  is  uninterrupted;  interruption  initiates 
a  wave  of  disintegration  which  may  involve  the  entire 
film-structure  of  the  protoplasm. 

In  the  cellular  elements  composing  typical  irritable 
tissues  like  muscle  and  nerve,  in  which  the  efTects  of 
stimulation  are  automatically  reversed  when  stimulation 
ceases,  the  indications  are  that  an  essentially  similar 
process  of  film-disintegration  occurs  during  stimulation, 
but  with  the  difference  that  a  new  surface-film  is  immedi- 
ately re-formed.  Whether  the  effects  of  stimulation  are 
reversible  or  irreversible  appears  to  depend  on  the 
ability  of  the  protoplasmic  system  to  re-form  the  structure 
necessary  for  stimulation.  Under  abnormal  conditions, 
e.g.,  lack  of  oxygen,  presence  of  depressant  poisons,  or 
disease,  the  rate  of  metabolic  synthesis  may  be  insutficient 
for  complete  restoration  in  the  inter^-als  of  stimulation, 
and  in  such  cases  excessive  stimulation  may  lead  to  the 
death  of  the  cell.  But,  normally,  recovery  is  rapid  and 
complete  in  irritable  elements  of  this  class;  as  already 
pointed  out,  the  indications  are  that  the  new  film-struc- 
ture is  formed  during  the  earlier  part  of  the  relative 
refractory  period. 

^Cf.  W.  B.  Hardy,  Journal  of  Physiology,  XIH  (1892),  165;  Tail, 
Quarterly  Journal  of  Experimental  Physiology,  XH  (1918),  42. 


350   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

The  ability  of  living  protoplasm  to  form  fresh  semi- 
permeable surface-films  at  cut  or  injured  surfaces  has 
long  been  known,  and  with  the  introduction  of  the 
methods  of  micro-dissection  this  property  has  lately 
become  the  subject  of  renewed  investigation/  The 
rate  and  other  features  of  the  film-forming  process  vary 
widely  in  different  forms  of  protoplasm,  and  also  in  the 
same  form  of  protoplasm  under  different  conditions; 
thus  it  is  less  active  in  cells  that  have  been  subjected  to 
abnormal  conditions  than  in  normal  and  "healthy" 
cells. ^  Apparently  this  process  is  of  the  same  nature  as 
the  reconstructive  change  occurring  at  the  surface  of 
irritable  elements  after  stimulation  and  occupying  the 
first  part  of  the  relative  refractory  period.  In  many 
respects  the  refractory  period  resembles  a  brief  period 
of  fatigue;  and  it  is  well  known  that  rapid  recovery 
from  fatigue,  i.e.,  a  complete  restoration  of  the  state 
preceding  stimulation,  requires  that  the  supply  of  oxygen 
and  the  other  environmental  conditions  should  be  normal. 
In  the  absence  of  these  conditions  excessive  stimulation 
may  lead  rapidly  to  the  physical  disorganization  and 
death  of  the  protoplasm.  Some  of  the  effects  of  extreme 
fatigue  (e.g.,  development  of  acid  reaction,  rapid  onset 
of  rigor)  resemble  those  produced  by  cytolytic  agents; 
and  it  is  possible  that  certain  metaboUc  products  formed 
during   activity   have   themselves   a   directly   cytolytic 

^  Cf .  Chambers,  American  Journal  of  Physiology,  XLIII  (191 7))  i, 
for  a  description  of  film-formation  after  injury  in  egg  cells.  Also  Jour. 
Gen.  Physiol.,  V  (1922),  189. 

2  Seifriz  {Annals  of  Botany,  CXXXVIII  [1921],  269)  cites  numerous 
observations  on  film-formation  in  protoplasm  under  various  conditions; 
cf.  also  his  article  in  Botanical  Gazette,  LXX  (1920),  360. 


MEMBRANE  CHANGES  DURING  STLMm.ATION   351 

effect.  Hence,  their  removal,  independently  of  other 
conditions,  is  favorable  to  recovery.  But  the  nviin 
factor  in  the  reversal  of  the  effects  of  stiniuhition,  normal 
or  abnormal,  appears  to  be  the  synthetic  or  structure- 
forming  (formative)  metabolism  of  the  protoplasm. 
When  the  metabolic  rate  is  rapid,  recovery  from  stimula- 
tion or  injury  is  prompt  and  complete,  and  vice  versa. 
The  difference  between  the  recuperative  and  regenerative 
powers  of  young  and  old  individuals  in  higher  animals 
illustrates  this  condition. 

STIMULATING  EFFECTS  OF  PERMEABILITY-INCREASING 

AGENTS 

Chemical  or  physical  agents  whose  primar>^  effect  is 
to  increase  the  permeability  of  the  cell  surface  to  water- 
soluble  substances  have  as  a  class  a  strongly  stimulating 
action  -on  many  irritable  forms  of  protoplasm.  The 
physiological  effects  produced  by  salts  and  combinations 
of  salts  in  isotonic  solution  illustrate  this  very  clearly. 
Thus  pure  solutions  of  neutral  alkali  salts,  e.g.,  NaCl, 
have  in  general  a  rapid  permeability-increasing  action 
on  living  cells;  this  effect,  if  unreversed,  is  equivalent 
to  toxic,  and  is  prevented  by  the  addition  of  a  small 
proportion  of  CaCL  or  similarly  acting  salt  to  the  solu- 
tion; the  antagonistic  or  '' anti-toxic"  action  of  the 
latter  salt  is  to  be  referred  chiefly  to  this  preventive 
influence,  which  is  equivalent  to  protective  or  anti- 
cytolytic.  Correspondingly,  pure  solutions  of  Na  salts 
cause  stimulation  or  activation  in  many  cells;  and  this 
effect  also  is  prevented  by  addition  of  calcium  in  propor- 
tions similar  to  those  required  to  prevent  increase  of  per- 
meability.    The  twitching  of  vertebrate  skeletal  muscle 


352    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

in  pure  NaCl  solutions  has  been  well  known  since 
Sidney  Ringer's  time:^  this  solution  also  causes  rhythmi- 
cal stimulation  in  motor  nerve,  although  with  a  somewhat 
prolonged  latent  period;^  in  both  cases  the  effect  is 
prevented  by  the  presence  of  a  little  CaCla.  The 
muscle  cells  of  marine  animals  are  also  powerfully 
stimulated  by  pure  isotonic  NaCl;  an  especially  instruc- 
tive case  is  furnished  by  the  larva  of  the  annelid  Arenicola, 
in  which  the  contraction  in  the  pure  NaCl  solution  is 
very  energetic.  The  body-cells  of  this  organism  contain 
a  yellow  pigment  which  serves  as  an  indicator  of  increase 
of  permeability.  In  the  pure  NaCl  solution  the  pigment 
diffuses  into  the  surroundings  simultaneously  with  the 
contraction;  and  under  a  wide  range  of  conditions  the 
permeability-increasing  and  the  stimulating  effects  of 
different  salt  solutions  have  been  found  to  run  closely 
parallel.  Thus  both  effects  are  prevented  or  diminished 
by  the  addition  of  CaCla  or  MgCla  to  the  pure  Na-salt 
solution;  and  the  addition  of  organic  anaesthetics  in 
the  anaesthetizing  proportions  has  a  similar  action.^ 
Similarly  pure  isotonic  alkali  salt  solutions  cause  activa- 
tion and  increase  of  permeabiHty  in  unfertilized  starfish 
and  sea-urchin  eggs,  and  both  effects  are  prevented  by 
calcium  salts  or  anaesthetics."* 

In  general,  any  condition  that  prevents  or  retards 
the  increase  of  permeability  normally  produced  by  the 
pure  salt  solution  prevents  or  diminishes  stimulation. 
The  anti-stimulating  or  narcotic  action  of  compounds 

^  Cf.  chap.  viii. 

*  Mathews,  American  Journal  oj  Physiology,  XI  (1904),  455. 

3  Cf.  chaps,  viii,  ix. 

4  Cf.  p.  166. 


MEMBRANE  CHANGES  DURING  STIMUI.ATION    353 

like  the  organic  ancxsthetics  or  Mg  salts  ai)i)ears  to  be 
associated  with  a  characteristic  action  on  the  j)r()to- 
plasmic  surface-fihiis;  the  latter  are  rendered  more 
stable,  i.e.,  protected  against  the  permeability-increasing 
or  disintegrative  action  of  the  pure  salt  solution;  as 
we  have  seen,  a  definite  antitoxic  influence  is  exerted 
by  these  compounds  when  they  are  added  in  a])pn)j)riate 
concentrations  to  the  pure  salt  solution.  It  is  probable 
that  this  stabilizing  influence  is  responsible  for  the  general 
narcotizing  properties  of  such  compounds,  since  any 
condition  preventing  alteration  of  the  surface-films  must 
by  that  very  action  prevent  stimulation,  which  is 
dependent  upon  such  alteration. 

The  activating  effect  of  pure  alkali-salt  solutions 
upon  the  unfertilized  eggs  of  marine  animals  is  a  phe- 
nomenon which  has  many  important  physiological 
affinities  with  stimulation,  and  is  exhibited  under 
similar  conditions.  If  starfish  eggs  are  placed  in  pure 
isotonic  solution  of  NaCl  (or  similar  salt)  for  five  to  ten 
minutes  (at  20°)  and  are  then  returned  to  sea  water,  a 
considerable  proportion  form  fertilization-membranes 
and  cleave,  or  even  develop  to  a  free-swimming  stage.* 
But  the  same  solution  to  which  CaCL>  has  been  added 
(i  moL  to  20  alkah  salt)  has  little  or  no  effect.^  The 
eggs  of  Arbacia  are  more  resistant  to  this  ty})e  of  salt 
action,  and  are  only  slightly  affected  by  NaCl  solution; 
but  pure  isotonic  solutions  of  more  energetically  acting 
alkah  salts,  especially  the  iodides  and  thiocyanates  of 
Na  and  K,  form  fertilization-membranes  and  initiate  the 
activation-process  in  the  same  manner  as  other  c>'tolytic 

^American  Journal  of  Physiology,  XX\'I  (1910),  106. 
^  Ibid. ,XXV1I  (1911),  289. 


354   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

agents;^  in  these  eggs  an  after-treatment  with  hypertonic 
sea  water  is  required  to  complete  the  activation.  Solu- 
tions of  these  salts  containing  CaCls  or  MgCL  are 
ineffective;  pure  isotonic  solutions  of  CaCla  and  MgClj 
also  fail  to  induce  activation;  apparently  the  initial 
effect  of  the  activating  agent  must  be  to  increase  permea- 
bility, while  the  alkali  earth  salts  have  the  reverse  effect. 
This  is  probably  the  reason  why  when  added  to  the  pure 
alkali  salt  solution  they  counteract  those  effects  (activa- 
tion, stimulation,  and  toxic  action)  which  are  dependent 
on  increase  of  permeabihty. 

That  the  initial  effect  produced  by  the  pure  alkali 
salt  solution  is  a  permeability-increasing  one  is  to  be 
inferred  from  the  general  nature  of  the  action  of  such 
solutions  on  living  cells.  The  evidence  is  more  direct 
in  the  case  of  pigmented  eggs  like  those  of  Arhacia,  in 
which  the  pigment  visibly  dift'uses  into  the  surrounding 
pure  solution  (of  NaT,  KCNS,  etc.)  after  a  few  minutes' 
immersion.  In  the  Ca-containing  solution  this  effect  is 
absent;  the  permeability-increasing  and  the  activating 
effects  are  thus  simultaneously  prevented.  A  similar 
though  less  complete  preventive  effect  is  produced  by 
various  anaesthetizing  compounds,  especially  higher 
alcohols;  these  when  present  in  the  anaesthetiz- 
ing concentrations  (i.e.,  those  which  arrest  cell- 
division  reversibly)  retard  or  prevent  the  permeability- 
increasing  and  activating  action  of  the  pure  solu- 
tions.^ 

Loeb's  extensive  researches  on  artificial  partheno 
genesis    have    shown    conclusively    that    permeability- 

^  Journal  of  Morphology,  XXII  (1911),  695. 
^Journal  of  Experimental  Zoology,  XVI  (1914),  591. 


MEMBRANE  CHANGES  DURING  STLMULATION    355 

increasing  substances  in  general  (equivalent  to  c>'t(jlytic 
with  long-continued  action),  whatever  their  special 
chemical  nature,  have  the  same  activating  efTect  on  sea- 
urchin  eggs.'  The  substances  used  included  numerous 
lipoid-solvent  organic  compounds,  acids,  bases,  soaps, 
alkaloids,  cytolytic  glucosides  (saponin,  etc.),  and 
foreign  blood  sera.  A  brief  or  superficial  c>'tolytic 
action  is  thus  regarded  by  Loeb  as  the  initial  or  critical 
change  in  activation.  This  use  of  the  term  "c>'tolytic" 
seems,  however,  to  be  open  to  objection,  since,  as  usually 
employed,  it  imphes  an  irreversible  or  destructive 
effect  on  the  cell;  whereas  the  primary-  or  critical  change 
produced  in  activation  is  apparently  a  brief  temporary 
increase  of  surface-permeability  resulting  from  a  raj^dly 
reversed  breakdown  of  the  protoplasmic  surface  layer. 
The  connection  between  this  effect  and  activation  is 
undoubtedly  highly  indirect  and  complex;  but  the  same 
may  be  said  for  the  connection  between  the  direct  action 
of  any  stimulating  agent  on  an  irritable  tissue  and  the 
succeeding  response  of  the  latter.  What  is  significant 
is  that  in  both  cases  the  primary  or  initiator}-  change  in 
the  complex  physiological  sequence  appears  to  consist 
in  a  temporary  disruption  or  breakdown  (an  elTect 
probably  related  to  de-emulsiiication)  of  the  protoplasmic 
surface  layer.  This  change  furnishes  the  releasing 
condition  for  those  metabolic  and  other  processes  of 
which  the  characteristic  vital  "response"  is  the  eventual 
and  biologically  important  consequence  or  expression. 
Physical  agents  like  ultra-violet  radiation  or  heat 
(30-40°),  which  also  cause  cytolysis  in  unfertilized  eggs 

^  Artificial  Parthenogenesis  and  Fertilization,  University  of  Chicago 
Press  (1913). 


356    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

and  other  cells,  exhibit  under  appropriate  conditions  a 
similar  activating  influence.^ 

INCREASE  OF  PERMEABILITY  DURING  NORMAL  STIMU- 
LATION, ACTIVATION,  AND  CELL-DIVISION 

Direct  proof  of  the  increased  permeability  of  rapidly 
responding  tissues  like  vertebrate  muscle  or  nerve 
during  normal  stimulation  is  difficult  to  obtain.  In  the 
case  of  muscle  the  results  gained  with  the  method  of 
electrical  conductivity^  are  of  uncertain  value,  since  the 
change  in  the  form  of  the  tissue,  the  production  of 
electrolytes  (e.g.,  lactic  acid)  in  the  process  itself,  and 
the  change  in  the  distribution  or  quantity  of  the  inter- 
cellular fluids  (lymph),  all  affect  the  total  conductivity; 
hence  the  observed  alterations  may  depend  on  other 
factors  than  the  changing  permeability  of  the  plasma 
membranes.  Direct  observation  of  the  penetration  of 
easily  detectable  compounds  into  the  muscle  cell  has 
given  better  results;  recently  Mitchell  and  his  associates^ 
have  shown  that  rubidium  and  caesium  chlorides  do  not 
enter  the  muscle  cells  when  the  resting  muscle  is  perfused 
with  Ringer's  solution  containing  these  salts,  but 
penetrate  readily  when  the  tissue  is  thrown  into  contrac- 
tion by  stimulating  the  nerve.  In  this  case  there  seems 
to  be  an  unequivocal  demonstration  of  increased  permea- 
biHty  to  inorganic  salts  during  stimulation.     Embden 

^  For  the  activation  of  starfish  eggs  by  heat  cf.  Delage,  Arch.  zool. 
exper.  et  gen.,  IX  (1901),  Series  III,  285;  R.  S.  Lillie,  Journal  of  Experi- 
mental Zoology,  V  (1908),  375;  Biological  Bulletin,  XXVIII  (1915),  260. 
For  the  action  of  ultra-violet  rays  cf.  J.  Loeb,  Science,  XL  (1914),  680; 
R.  S.  Lillie,  American  Journal  of  Physiology,  LX  (1922),  57,  272. 

2  Cf .  McClendon,  American  Journal  oj  Physiology,  XXIX  (19 12), 
302. 

3  Mitchell,  Wilson,  and  Stanton,  Jour.  Gen.  Physiol.,  IV  (192 1),  141. 


MEMBR.\NE  CHANGES  DURING  STLMULATION   357 

finds  that  frogs'  muscle  gives  olT  inorganic  phosphate 
to  the  medium  during  contraction  but  not  during  rest, 
and  he  regards  this  fact  as  further  evidence  of  an  increase 
of  permeabiHty  during  stimulation.' 

In  nerve  evidence  of  increased  permeability  during 
stimulation  is  seen  in  a  characteristic  decrease  in  the 
electrical  polarizabiHty  of  the  tissue.  \\  hi-n  a  current 
from  a  battery  is  passed  by  non-polarizable  electrodes 
through  any  living  tissue,  a  counter  electromoti\c  force 
is  immediately  set  up  in  the  tissue,  so  that  when  the  latter 
is  connected  with  a  galvanometer  (preferably  through 
a  double  key  w^hich  simultaneously  breaks  the  polarizing 
circuit  and  opens  the  circuit  through  the  galvanometer) 
a  temporary  current  is  observed  flowing  in  the  reverse 
direction.  This  current,  the  polarization  current,  has 
its  source  within  the  tissue  at  the  regions  of  entrance  and 
exit  of  the  original  or  polarizing  current.  Apj^arently 
the  characteristically  high  resistance  of  living  cells  and 
tissues  to  the  electric  current  is  largely  or  mainly  a  result 
of  this  polarization,  since  the  resistance  to  rapidly 
alternating  currents  (which  cause  little  or  no  polarization) 
is  found  to  be  much  less  than  to  direct  currents.  The 
indications  are  that  the  semi-permeable  membranes  of 
the  living  cells  are  the  chief  seat  of  the  polarization; 
when  semi-permeability  is  lost,  as  at  death,  polarizability 
is  greatly  diminished  or  disappears.  Some  fifty  years 
ago  Griinhagen  and  Hermann  observed  that  batters- 
currents  flowing  through  a  nerve  underwent  an  increase 
when  the  nerve  was  stimulated;  and  the  most  j^robable' 

^  Embden,  Berichte  iihcr  d.  ges.  Physiol.,  II  (1920),  159. 

'  Cf .  Hermann,  "Das  galvanische  Vcrhaltcn   cincr  durch  '  n 

Nervenstrecke  wahrend  der  Erregung,"  Arch.  ^f5.  Physiol.,  \i  v-  , -;), 
560;  cf.  also  ibid.,  X  (1875),  215- 


358   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

interpretation  of  this  effect  is  that  it  is  an  expression  of 
decreased  polarizability.  This  view  is  confirmed  by 
Bernstein's  observation  that  the  electrotonic  currents  of 
nerve,  which  are  undoubtedly  polarization  currents,  are 
also  decreased  during  stimulation/  Any  such  decrease 
of  polarizability,  in  a  system  partitioned  by  membranes, 
is  an  indication  of  increased  permeability  of  the  mem- 
branes to  ions.  Recently  Ebbecke  has  again  shown  that 
the  polarizability  of  nerve  is  decreased  during  stimula- 
tion;^ he  has  also  found  that  the  same  is  true  of  the 
epidermal  cells  of  the  human  skin,  and  he  has  discovered 
various  interesting  parallels  between  the  phenomena 
exhibited  by  nerve  and  by  skin,  respectively,  during  and 
after  the  passage  of  the  electric  current.^  The  polariza- 
bility of  the  skin  and  its  resistance  to  constant  currents 
are  greatly  decreased  by  either  mechanical  or  electrical 
stimulation,  and  this  effect  is  independent  of  variations 
of  vascularity  or  other  extracellular  conditions.  The 
reactions  to  the  constant  current  are  also  typical: 
opposite  effects  are  produced  at  anode  and  cathode, 
as  in  the  polar  stimulation  of  irritable  tissues,  and  the 
action  of  salts  and  anaesthetics  on  the  skin  is  analogous 
to  that  observed  with  other  irritable  tissues  and  cells; 
e.g.,  conductivity  is  increased  by  solutions  of  Na  and  K 
salts  and  decreased  by  Ca  salts  and  anaesthetics."*   These 

^  Bernstein,  Arch.  Anat.  Physiol.  (1866),  p.  614;  also  Elektrobiologie, 
chap,  vii,  p.  130.  Cf.  also  Gotch's  article  in  Schafer's  textbook,  II, 
547  ff- 

2  Ebbecke,  " Membrananderung  und  Nervenerregiing,"  Arch.  ges. 
Physiol.,  CXCV  (1922),  555. 

3  Ebbecke,  Arch.  ges.  Physiol.,  CXCV  (1922),  300,  324. 
<  Ebbecke,  ibid.,  CXC  (1921),  230;  cf.  pp.  247  fif. 


MEMBRANE  CHANGES  DURING  STLMULATIOX    359 

effects  receive  a  consistent  explanation  on  the  theory  of 
variations  of  permeability. 

The  implication  that  apparently  inert  cells  like 
epidermal  cells  are  irritable,  in  the  same  sense  as  muscle 
and  nerve,  may  seem  a  strange  one,  but  it  is  in  harnKjny 
with  the  general  conception  of  irritability  as  an  ele- 
mentary property  of  all  forms  of  living  matter.  Waller 
has  pointed  out  that  the  most  certain  ''sign  of  life"  in  an 
apparently  inert  animal  or  plant  tissue  is  the  elicitaticjn 
of  an  electric  response  C' blaze-current")  on  mechanical 
stimulation.^  The  increased  proliferative  activity  of 
the  epidermal  cells  of  the  skin  after  hard  mechanical 
usage  is  well  known.  Ebbecke's  experiments  show  that 
such  treatment  increases  the  electrical  conductivity; 
in  other  words,  increases  permeability  and  decreases 
polarizability,  as  in  other  cases  of  stimulation.  The 
increased  growth  is  the  expression  of  this  stimulation. 

Recent  observations  by  Crozier^  have  also  a  bearing 
on  the  present  problem.  He  fmds  that  electrical 
stimulation  causes  a  well-marked  increase  in  the  i^ermea- 
bility  of  the  mantle-cells  of  nudibranchs  to  acids;  in 
these  cells  the  degree  of  permeability  can  be  measured 
by  the  time  required  to  change  the  color  of  an  intracellular 
pigment,  which  acts  as  a  natural  indicator.  Mg  salts 
and  anaesthetics  (in  appropriate  concentrations)  were 
found  to  decrease  permeability,  as  in  the  cases  already 
cited.^  Mechanical  traction  causes  an  increase  of 
permeability,  which  within  certain  limits  is  reversible. 
These  observations   throw  much  light  on   the  general 

^  Waller,  Signs  of  Life. 

^Jour.  Gen.  Physiol,  IV  (1922),  723. 

3  Cf.  chap.  viii. 


360   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

conditions  of  mechanical  stimulation;  related  observa- 
tions are  those  of  Carlson,  v/ho  observed  that  increasing 
the  mechanical  tension  of  the  heart-ganglion  of  Limulus 
increased  the  rate  of  nervous  discharge;^  and  in  frog's 
muscle  it  has  been  found  that  stretching  causes  an 
increase  in  the  production  of  CO2  and  lactic  acid.^ 
Increase  of  permeability  is  probably  a  factor  in  both  of 
these  effects. 

The  effects  of  mechanical,  electrical,  thermal,  and 
other  changes  of  physical  condition  on  indifferent  or 
unspecialized  cells  of  various  kind  (blood  corpuscles, 
egg-cells,  epithelial  cells,  etc.)  all  have  a  bearing  on  the 
question  of  the  relation  of  permeabihty-change  to 
stimulation.  The  constant  current  causes  polar  dis- 
integration in  many  cells,  an  effect  analogous  to  polar 
stimulation;  similarly  it  causes  polar  secretion  in  cutane- 
ous and  mucous  gland  cells.^  The  laking  of  blood 
corpuscles  by  induction  shocks  has  also  evident  analogies 
to  electrical  stimulation. 

There  is  abundant  evidence  of  an  increase  in  the 
permeabihty  of  the  surface  layer  of  many  egg  cells  during 
the  early  stages  of  normal  fertilization.  In  some  cases 
the  surface  protoplasm  undergoes  extensive  alteration 
and  there  results  a  visible  loss  or  secretion  of  material  to 
the  exterior  {Nereis,  lamprey,  frog).'*    In  the  sea-urchin 

^  Carlson,  American  Journal  of  Physiology,  XVIII  (1907),  149. 

'  Eddy  and  Downs,  American  Journal  of  Physiology,  LVI  (1921),  188. 

3  Loeb,  Arch.  ges.  Physiol. ^  LXV  (1896),  308. 

4  Cf.,  for  Nereis,  F.  R.  Lillie,  Journal  of  Experimental  Zoology, 
XII  (191 2),  414;  for  the  lamprey,  Bataillon,  Arch,  de  zool.  exper.  et 
gen.,  VI  (1910),  Series  5,  128;  for  frog,  Backmann  and  Runnstrom, 
Arch.  ges.  Physiol.,  CXLIV  (191 2),  287. 


MEMBRANE  CHANGES  DURING  STLMULATIOX    361 

egg  the  space  between  the  fertilization-menibranc  and 
the  egg  surface  contains  a  colloidal  substance  which  is 
apparently  separated  from  the  egg  at  fertilization.* 
Lyon  has  also  observed  an  increased  loss  of  catalase  at 
this  time.^  McClendon  and  Ciray  have  shown  that  a 
significant  increase  in  electrical  conductivity  occurs  in 
the  sea-urchin  egg  immediately  after  fertilization.^ 
Increase  in  the  rate  of  entrance  of  dyes,  and  apparently 
also  of  toxic  substances,  has  also  been  observed.-'  In  the 
Arbacia  egg  the  rate  of  exchange  of  water  in  hyj)ertonic 
or  hypotonic  media  is  increased  several  times  as  a  result 
of  fertilization. 5  A  change  in  the  protoi)lasmic  surface 
layer,  associated  with  increased  permeability  to  water 
and  water-borne  substances,  thus  appears  to  be  a  \ery 
general  accompaniment  of  both  nonnal  and  artificial 
activation.  These  facts,  taken  as  a  whole,  suggest  that 
the  first  stage  of  the  activation-process  consists  in  a 
breakdown,  followed  immediately  by  a  re-formation,  of 
the  external  protoplasmic  layer  or  plasma  membrane. 

Recent  observations  by  Just^  have  emphasized  still 
more  fully  the  resemblance  between  the  primary  or 
surface  change  in  the  activation  of  egg  cells  and  in  the 
stimulation  of  irritable  tissues.  In  the  large  egg  of  the 
sand-dollar,    Echinaradniius    {ca.    140  ju    in    diameter). 

^  Cf.  Loeb,  Parthenogenesis  and  Fertilization,  chap.  .\x,  p.  20S. 

2  Lyon,  American  Journal  of  Physiology,  XXV  (1909),  199. 

3  McClendon,  American  Journal  of  Physiology,  XW'II  (1910),  240; 
J.  Gray,  Jour.  Mar.  Biol.  Assoc,  X  (1913),  50- 

"McClendon,  loc.  cit.;  Lyon  and  ShackcU,  Science,  XXXII  (1910), 
249;  Harvey,  Science,  XXXII  (1910).  S^S- 

sAfnerican  Journal  of  Physiology,  XL  (1916),  249. 
6  Just,  ibid.,  LX  (1922),  516. 


362    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

the  first  visible  effect  of  insemination  is  an  alteration  of 
the  egg  surface,  beginning  at  the  point  of  entrance  of 
the  spermatozoon.  A  liquefactive  or  secretory  change 
occurs  in  the  protoplasmic  surface  layer,  in  consequence 
of  which  a  thin  surface-film  is  separated  to  form  the 
fertilization  membrane;  this  process  of  separation  is  not 
simultaneous  at  all  points  on  the  surface,  but  progresses 
in  a  wavelike  manner  from  the  point  of  sperm-entry 
to  the  opposite  pole,  which  it  reaches  about  20  seconds 
later  (at  20°).  During  the  propagation  of  this  dis- 
turbance over  the  egg  surface,  the  latter  is  altered  in 
such  a  manner  that  the  plasma  membrane  loses  tempora- 
rily its  normal  tenacity  and  coherence;  this  effect  is 
readily  demonstrated  by  placing  the  eggs  at  this  time 
in  dilute  sea  water  (60  vols,  fresh  plus  40  sea  water) 
in  which  they  undergo  immediate  and  rapid  disintegra- 
tion. The  breakdown  of  the  surface  layer  can  be  seen 
to  begin  at  the  region  where  the  fertilization  membrane 
is  beginning  its  separation.  This  period  of  instability 
lasts  only  for  the  brief  period  (about  one  minute)  during 
which  the  "cortical  reaction"  is  traveling  over  the  egg 
surface;  within  about  a  minute  after  insemination  the 
original  resistance  to  dilute  sea  water  has  returned, 
showing  a  restitution  of  the  normal  coherent  surface  layer. 
Thus  a  characteristic  surface-change,  apparently  accom- 
panied by  a  local  disintegration  or  disorganization  of  the 
plasma  membrane,  constitutes  the  first  reaction  of  this 
egg  to  fertilization;  this  change  is  propagated  as  a  wave 
over  the  cell  surface  and  is  followed  by  a  reconstructive 
process  restoring  the  original  condition.  As  we  have 
already  seen,  there  are  indications  that  a  propagated 
surface-change  of  a  similar  kind,  only  with  dift'erent  time- 


MEMBRANE  CHANGES  DURING  STIMULATION    363 

relations  and  a  different  velocity  of  pro])af^ation,  accom- 
panies stimulation  in  irritable  cells  and  nerve  fibers. 

During  the  formation  of  the  cleavage-furrow  in  cell- 
division  a  similar  reversible  change  in  the  i)hysical 
consistency  and  coherence  of  the  cell  surface  occurs  in 
echinoderm  eggs;'  and  there  are  many  indications  that 
the  same  kind  of  change  is  of  general  occurrence  in 
dividing  cells.  The  case  of  cell-division  is  of  special 
interest,  since  a  rhythm  of  chemical  change  and  of 
susceptibility  to  physical  and  chemical  injury  is  also 
associated  with  the  rhythm  of  the  cleavage-process. 
Lyon's  experiments  indicate  that  at  the  time  when  the 
cleavage-furrow  is  forming  in  the  Arbacia  egg,  the  rate  of 
evolution  of  CO2  is  several  times  greater  than  in  the  inter- 
vals between  cleavage;^  at  this  time  the  egg  is  also  most 
susceptible  to  injury  by  heat,  ultra-violet  radiation, 
deprivation  of  oxygen,  and  poisons  (KCN.  acids,  and 
organic  compounds).  The  time-relations  of  the  accom- 
panying change  in  the  plasma  membrane  can  be  followed 
readily  and  accurately  by  transferring  successive  portions 
of  a  single  lot  of  recently  fertihzed  Arbacia  eggs  (in  which 
the  cleavage-process  is  very  regular  and  occurs  simultane- 
ously in  all  eggs)  from  normal  sea  water  to  dilute  sea 
water  (50  to  60  volumes  fresh  water  in  100  of  the  mixture) 
at  regular  intervals  before,  during,  and  after  the  for- 
mation of  the  cleavage-furrow.^  Eggs  which  are  thus 
treated  some  time  before  cleavage  swell  osmotically  but 
without   undergoing   evident   increase   of   permeability 

»R,  S.  Lillie,  Journal  of  Experimental  Zool.,  XXI  (191^),  M^l 
Herlant,  Comp.  rend.  soc.  bioL,  LXXXI  (191S),  151;  J"st,  .-ImmVufi 
Journal  of  Physiology,  LXI  (1922),  505. 

^  Lyon,  loc.  cit.  ^  R.  S.  Lillie,  loc.  cit. 


364    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

or  losing  the  power  of  development  on  return  to  sea 
water;  at  about  the  time  when  the  furrow  begins 
to  form,  there  is  a  marked  and  rapid  decline  of  extensi- 
bihty  and  coherence  in  the  plasma  membrane,  and  the 
eggs  show  rapid  loss  of  pigment  and  cytolysis  when 
transferred  to  the  dilute  sea  water.  Eggs  brought  into 
dilute  sea  water  a  few  minutes  after  the  furrow  is  complete 
are  found  to  have  recovered  the  original  resistance,  and 
swell  without  cytolysis.  These  experiments  show  clearly 
that  accompanying  the  division  of  the  cell  body  there 
is  a  reversible  change  in  the  properties  of  the  plasma 
membrane,  this  change  involving  both  loss  of  coherence 
and  increase  of  permeabihty.  That  the  permeabihty  as 
well  as  the  physical  tenacity  of  the  membrane  is  altered 
is  best  shown  by  studying  the  behavior  of  the  eggs  in 
concentrated  instead  of  dilute  sea  water;  during  the 
formation  of  the  furrow  the  abstraction  of  water  and 
shrinkage  are  distinctly  less  rapid  and  complete  than 
before  or  after  cleavage,  a  difference  indicating  a  partial 
loss  of  semi-permeabiKty  at  this  time.  Other  indications 
of  increase  of  permeabihty  during  cleavage  have  been 
noted  by  various  observers  (Harvey,  Just,  Lyon). 

According  to  the  present  theory  variations  of  electrical 
surface-potential  should  accompany  these  changes  of 
permeabihty;  and  observations  made  at  Woods  Hole 
in  1904  by  Miss  Hyde,'  using  fish  eggs,  indicate  that 
during  the  formation  of  the  cleavage-furrow  the  blasto- 
disk  area  becomes  increasingly  negative  relatively  to  the 
general  surface  of  the  egg.  Experiments  in  this  field 
are,  however,  few  in  number  as  yet;  and  it  would  be 
desirable  to  repeat  and  extend  these  observations,  using 

» I.  H.  Hyde,  loc.  cii. 


MEMBRANE  CHANGES  DURING  STIMULATION    365 

the  thermionic  amplifier  to  enhance  the  minute  effects 
obtainable  from  single  eggs,  and  the  string  gal\-anomctcr 
as  the  recording  instrument.  It  should  be  noted, 
however,  that  Miss  Hyde's  observations  are  in  conformity 
with  those  of  other  investigators  who  have  found  rapidly 
growing  regions  of  plants  and  animals— i.e.,  those  where 
cell-division  is  in  active  progress — to  be  electrically 
negative  to  more  slowly  growing  regions.' 

Evidence  that  reversible  variations  of  permeability 
are  associated  with  such  processes  as  fertilization  and  cell- 
division  may  seem  to  have  a  somewhat  indirect  bearing  on 
the  problem  of  the  conditions  of  stimulation  in  t}^)ical  ir- 
ritable tissues  hke  muscle  and  ner\'e.  Yet  all  of  these  vital 
processes  are  alike  in  being  subject  to  initiation  or  control 
by  environmental  conditions  or  events;  in  other  words, 
they  all  illustrate  the  characteristic  ''irritability"  of 
living  matter.  The  fundamental  conditions  determining 
and  controlling  the  metabolic  reactions  which  furnish 
the  energy  for  vital  processes  are  in  all  probability  every- 
where the  same.  Hence  the  above-cited  facts  indicating 
that  changes  of  permeabihty  are  regular  accompaniments 
of  fertilization  and  cell-division  are  confirmatory  evidence 
for  the  view  that  such  changes  play  an  essential  part  in 
other  manifestations  of  irritability.  In  all  forms  of 
protoplasm  the  essential  metabolic  reactions  occur 
under  the  control  of  the  film-partitioned  or  emulsion-like 
structure  of  the  living  system;  it  is  therefore  to  be 
expected  that  they  will  vary  in  their  rate  and  character 

»Cf.  Hermann  and  Muller-Hcttlingcn,  Arch.  gcs.  Physiol.,  XXXI 
(1883),  193;  A.  P.  Mathews,  American  Journal  of  Physiology,  VIII 
(1903),  294;  C.  M.  Child,  Biological  Bulletin,  XL!  (1921),  9°;  t-  J- 
Lund,  Journal  of  Experimental  Zoology,  XXXVI  (19"),  477;  Hyman 
and  Bellamy,  Biological  Bulletin,  XLIII  (192^),  3U- 


366    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

with  alterations  in  this  structure.  In  particular  the  fore- 
going evidence  indicates  that  the  temporary  breakdown 
of  the  semi-permeable  surface-lamella  or  limiting  layer 
of  the  protoplasmic  emulsion  influences  profoundly  the 
chemical  and  other  processes  occurring  in  the  cell 
interior;  apparently  the  effects  of  this  surface-change 
are  transmitted  throughout  the  whole  mass  of  protoplasm, 
and  the  physiological  activities  of  the  cell  are  changed 
correspondingly. 

It  has  already  been  mentioned  that  experiments  of  a 
kind  closely  analogous  to  those  described  for  unfertihzed 
egg  cells  may  be  performed  with  irritable  tissues  like 
muscle  and  nerve,  both  of  which  when  immersed  in 
pure  isotonic  solutions  of  neutral  sodium  salts  undergo 
rhythmical  or  other  stimulation,  which  may  be  checked 
by  calcium  salts  or  anassthetics;  and  the  above-cited 
experiments  with  Arenicola  larvae  afford  other  and  more 
direct  evidence  that  stimulation  and  permeabiHty- 
increase  are  closely  associated.  Hober's  experiments  on 
the  influence  of  anaesthetics  in  checking  the  development 
of  the  negative  electrical  variation  produced  in  muscle 
by  apphcation  of  KCl  solution  furnish  evidence  of  a 
similar  kind.  The  effects  of  neutral  salts  may  thus 
be  more  or  less  completely  antagonized  by  anaesthetics 
as  well  as  by  the  alkali  earth  cations.  In  all  of  these  cases 
prevention  of  permeability-increasing  action  runs  parallel 
with  prevention  of  stimulation  or  of  the  normal  manifes- 
tations of  stimulation.^ 

Conversely  any  strongly  cytolytic  action  has  a  stimu- 
lating effect.  The  larvae  of  Arenicola  contract  strongly  in 
solutions  of  cytolytic  agents  like  chloroform;   this  effect 

^  Cf .  chaps  viii,  ix. 


MEJVIBRANE  CHANGES  DURING  STLMULATION    367 

is  irreversible  and  is  associated  with  a  marked  increase 
of  permeability  and  rapid  death.  Phenomena  of  a 
similar  kind  are  seen  in  vertebrate  skeletal  muscle. 
The  permanent  or  irreversible  shortening  or  "contrac- 
ture" of  frogs'  muscle  in  solutions  containing  cytolytic 
substances,  e.g.,  saturated  solution  of  chloroform  in 
Ringer's  solution,  is  well  known;  this  contraction  is 
associated  with  a  large  production  of  lactic  acid,  and 
apart  from  its  irreversible  or  ^' rigor"  character  bears 
many  resemblances  to  normal  contraction.  A  similar 
contraction  accompanies  the  onset  of  heat-rigor  and  other 
forms  of  death-rigor,  and  in  all  such  cases  the  structure 
of  the  cells  is  profoundly  altered,  the  permeability 
undergoing  marked  increase  while  the  iibrils  lose  their 
tensile  strength  and  elasticity.  These  changes  have  a 
close  general  resemblance  to  those  already  described  as 
accompanying  the  accelerated  rhythmical  activity — 
indicating  excessive  stimulation — of  the  ctenophore 
swimming  plate  in  pure  Na  salt  solutions. 

SENSITIZATION  AND  RELATED  EFFECTS 

The  foregoing  contraction-producing  action  of  cytoly- 
tic substances  on  frog's  muscle  may  be  made  to  resemble 
more  closely  the  phenomena  of  normal  stimulation  by 
first  ''sensitizing"  the  muscle  by  immersing  it  for  a  few 
minutes  in  a  pure  isotonic  solution  of  a  neutral  Xa  salt 
(NaCl,  NaBr,  Nal,  NaNO.,,  etc.).  The  fresh  isolated 
gastrocnemius  (normal  or  curarized),  immersed  in 
Ringer's  solution  and  arranged  so  as  to  write  upon  a 
smoked  drum,  is  transferred  for  four  or  live  minutes  to 
the  pure  solution  of  the  Na  salt,  from  which  it  is  brought 
directly    into    the    solution    containing    the    cytolytic 


368   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

substance.  The  contraction  then  resulting  is  much 
more  rapid  and  vigorous  than  in  the  control  muscle  which 
is  brought  into  the  same  solution  directly  from  Ringer; 
the  degree  of  permanent  shortening  is  also  greater,  as  is 
also  the  degree  of  coagulation  of  the  muscle  protoplasm, 
as  shown  by  the  whitening  or  opacity  produced.  The 
action  of  contraction-producing  salt  solutions  Kke  KCl, 
Na  tartrate,  sulphate,  and  citrate  is  similarly  intensified 
by  a  previous  bath  of  the  kind  above;  also  the  rapidity 
of  onset  of  heat-rigor,  with  the  associated  contraction, 
when  the  muscle  is  dipped  in  warm  Ringer's  solution 
(38'-4o°).  These  sensitization-effects  have  been  demon- 
strated with  the  following  cytolytic  substances:  chloro- 
form, cytolytic  glucosides  (saponin,  digitahn,  aconitin, 
and  agaricin),  tetanus  toxin,  rattlesnake  venom,  foreign 
blood  sera  (horse,  dog),  and  soaps.  The  degree  of  the 
stimulation  following  the  introduction  of  the  salt- 
sensitized  muscle  into  the  solution,  as  indicated  by  the 
rate  and  degree  of  the  contraction,  is  in  general  pro- 
portional to  the  intensity  of  the  cytolytic  action  (as 
shown  by  varying  the  concentration  and  nature  of  the 
cytolytic  substances)  .^ 

Since  in  all  such  experiments  the  contraction  follows 
immediately  (within  a  second  or  less)  after  placing  the 
muscle  in  the  stimulating  solution,  there  seems  to  be  no 
doubt  that  the  initiatory  effect  consists  in  an  alteration 
of  the  external  surface  layer  of  the  muscle  cells.  Appar- 
ently, when  the  normal  muscle  is  exposed  to  the  pure 
salt  solution,  the  cell  surface  is  rendered  more  susceptible  / 
to  alteration  by  external  chemical  agents,  and  the 
susceptibiHty  to  chemical  stimulation  of  the  kind  above 

^American  Journal  of  Physiology,  XXVIII  (191 1),  197;  cf.  p.  214. 


MEMBRANE  CHANGES  DURING  STIMULATION    369 

is  correspondingly  increased.  The  relative  insuscepti- 
bility of  the  normal  muscle  depends  on  the  presence  of 
Ca  salts  in  the  external  medium;  if,  instead  of  a  pure 
solution  of  the  sensitizing  salt,  one  containing  CaCl, 
(i  mol  CaClz  to  20  Na  salt)  is  used,  no  such  effects  arc 
obtained/  The  sensitizing  action  is  thus  sui)ject  to 
typical  salt-antagonism,  like  so  many  other  biological 
processes,  especially  those  involving  alteration  of  the 
protoplasmic  surface  layers.  Muscles  which  have  been 
rendered  hypersensitive  by  exposure  to  the  i)ure  salt 
solution,  rapidly  recover  their  normal  properties  on 
return  to  Ringer's  solution.  The  inverse  type  of  effect, 
decrease  of  susceptibihty  to  chemical  stimulation,  may 
be  induced  by  a  similar  exposure  to  isotonic  solutions 
of  CaCL,  MgClz  or  similar  salts.  Such  desensitizing 
effects  are  closely  related  to  those  classed  under  narcosis, 
depression,  or  anaesthesia,  and  are  also  reversible  in 
Ringer's  solution. 

A  related  type  of  salt  sensitization,  produced  by 
isotonic  solutions  of  Na  salts  whose  anions  precijMtate 
calcium  (or  remove  Ca  ions  from  solution),  was  described 
by  Loeb  in  1901.''  Muscles  dipped  for  a  few  minutes  in 
solutions  of  Na  sulphate,  tartrate,  citrate,  or  similar 
salt,  and  then  brought  into  the  air  (or  other  foreign 
medium,  e.g.,  oil),  exhibit  vigorous  tetanic  contractions, 
which  cease  or  are  diminished  on  return  to  the  salt 
solution.  Apparently  this  reaction  dei)ends  on  an 
altered  contact-sensibility,  due  to  some  modilication  of 
the  cell  surface.  It  illustrates  a  t\iie  of  effect  which 
appears  to  be  widely  prevalent  in  irritable  elements. 

» Unpublished  observations  in  the  Biological  Laborator>'  of  Clark 
University. 

2  J.  Loeb,  American  Journal  of  Physiology,  V  (190O,  362. 


370   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

Nerve  is  affected  similarly;  and  the  characteristic 
pharmacological  effects  produced  by  this  group  of  salts, 
e.g.,  their  cathartic  action  (which  apparently  depends 
upon  a  heightening  of  contact-irritability  in  the  intestinal 
tract),  are  probably  referable  to  conditions  of  a  similar 
kind.  There  is  much  evidence  that  many  forms  of 
pharmacological  action  are  due  to  changes  in  the  physical 
consistency,  permeabihty,  chemical  alterabihty,  or  other 
properties  of  the  protoplasmic  surface-films. 

It  is  important  to  note  the  relation  of  sensitizations 
of  the  class  described — which  consist  in  a  general  heighten- 
ing of  irritability  toward  non-specific  chemical  or  other 
stimulating  conditions — to  the  class  of  specific  sensitiza- 
tions, of  which  anaphylaxis  is  the  most  striking  example. 
The  general  features  of  this  phenomenon  are  well 
known.  During  the  early  stages  of  the  process  of 
immunization,  following  the  introduction  of  a  foreign 
protein  into  the  circulation,  the  cells  of  the  mammalian 
organism  become  highly  sensitive  to  the  introduction  of 
further  protein  of  the  same  kind,  and  in  certain  animals, 
notably  the  guinea-pig,  the  most  conspicuous  effect  of 
the  second  injection  is  seen  in  the  smooth  muscle  cells, 
especially  those  of  the  respiratory  tract;  these  contract 
firmly  and  persistently  and  occlude  the  bronchioles, 
with  death  by  asphyxiation  as  a  consequence.  This 
contraction-producing  effect  is  almost  certainly  depend- 
ent on  a  specific  antigen-anti-body  reaction  occurring 
in  the  surface  layer  of  the  muscle  cells.  The  promptitude 
with  which  it  follows  injection  of  even  a  small  quantity 
of  the  foreign  protein  indicates  this,  since  the  latent 
period  seems  insufficient  for  penetration  into  the  cell 
interior;    such   a   conclusion   receives   further   support 


MEMBRANE  CHANGES  DURING  STIMULATION 


^^ 


I 


from  the  facts  of  passive  sensitization,  in  wliich  liic 
sensitized  condition  is  produced  in  a  normal  j;cuinca-i)ij: 
by  injection  of  blood  from  another  animal  which  1: 
already  been  immunized  to  the  protein  in  questitm. 
Passive  sensitization  can  also  be  produced  in  vitro  by 
bathing  strips  of  uterus  with  serum  from  an  immunized 
animal.  The  most  probable  interpretation  of  this 
phenomenon  is  that  the  circulating  anti-body  is  adsorbed 
or  fixed  by  contact  with  the  smooth  muscle  cells,  thus 
becoming  a  constituent  of  the  protoplasmic  surface 
layer.  When  the  antigen  (the  original  protein  used  for 
immunization)  is  introduced,  it  reacts  with  the  adsorbed 
anti-body,  and  in  so  doing  alters  the  structure  or  con- 
sistency or  permeabihty  of  the  surface  layer  (very  much 
as  a  specific  cytolysin  would  do)  in  a  manner  corre- 
sponding to  strong  stimulation.  Contraction  then 
results;  and  since  the  antigen-anti-body  reaction  is  an 
irreversible  one,  the  muscle  cells  remain  firmly  and 
persistently  contracted,  with  results  fatal  to  the  animal. 
Dale  has  brought  forward  evidence  that  the  specific 
chemical  interaction  underlying  anaphylactic  shock  is 
identical  with  the  precipitin  reaction,  the  ditlerence 
being  that  the  reaction  occurs  within  the  cell  instead  of 
in  the  blood  stream.'  If  tliis  is  the  case,  it  is  easy  to 
understand  why  powerful  stimulating  effects  should 
result  from  precipitation  of  proteins  within  the  proto- 
plasmic surface-film,  since  such  a  process  must  alter 
the  structure  and  permeability  of  this  layer  and  hence 
act  as  a  stimulating  condition  in  the  same  manner  as 
any  other  cytolytic  change  would  do. 

»  Dale,  Croonian  Lecture,  Proceedings  of  I  lie   Royal  Society,  B,  XCI 
(1920),  126. 


372  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

According  to  this  conception  the  anaphylactic 
reaction  of  smooth  muscle  cells  becomes  an  example 
of  specific  chemical  stimulation,  dependent  on  the 
presence  of  specific  substances  (presumably  protein)  in 
the  surface  layer  of  the  reacting  cell;  these  substances 
react  with  substances  of  corresponding  or  complementary 
configuration  in  the  en\ironment,  and  hence  furnish 
the  conditions  for  a  highly  selective  and  specific  type 
of  response.  Presumably  other  forms  of  specific  chemical 
sensitivity  are  also  to  be  referred  to  the  presence  of 
specific  chemical  compounds  in  the  surface-films  of  the 
reacting  cells.  Such  a  conception  renders  clearer  the 
general  nature  of  the  relation  between  the  special 
chemical  sensitivity  exhibited  by  a  particular  species  of 
cell  and  its  specific  chemical  organization.  Any  change 
in  the  chemical  constitution  or  physical  state  of  the 
plasma  membrane  must  influence  irritability  and  hence 
the  other  properties  or  activities  controlled  by  this 
region  of  the  cell. 

OTHER  INDICATIONS  OF  THE  CONNECTION  BETWEEN 
INCREASE  OF  PERMEABILITY  AND  STIMULATION 

Certain  instances  of  stimulation-effects  which  are 
associated  with  an  evident  increase  of  surface- 
permeabihty  have  already  been  cited.  Perhaps  the 
clearest  instance  of  a  direct  dependence  of  a  normal 
functional  response  upon  a  sudden  increase  of  permea- 
bihty  is  seen  in  the  osmotic  motor  mechanisms  of  plants, 
such  as  the  Venus'  flytrap  and  the  sensitive  plant. 
In  the  latter  plant,  Mimosa  pudica,  the  leaves  are  kept 
in  the  normal  expanded  and  upright  position  by  turgid 
or  water-distended  masses  of  parenchyma  cells  (pulvini) 


MEMBRANE  CHANGES  DURING  STIMULATION    373 

at  the  base  of  each  leaflet  and  petiole.  This  turgor,  as 
in  other  herbaceous  tissues,  is  maintained  by  the  osmotic 
pressure  of  the  cell-contents;  this  pressure,  acting 
against  the  semi-permeable  plasma  membranes,  causes 
the  entrance  of  water  from  the  intercellular  s])aces  and 
distends  the  cells  until  the  pressure  is  equilibrated  by 
the  elastic  tension  of  the  stretched  ci-lhilose  cell  walls. 
Evidently  the  continued  maintenance  ol  this  condition 
depends  on  the  preservation  of  semi-permeability. 
On  stimulation  there  is  a  sudden  loss  of  turgor,  accom- 
panied by  exit  of  water  and  dissolved  substances  from 
the  cells;  the  stretched  cell  walls  of  the  puhini  contract, 
the  leaves  fall,  and  the  leaflets  fold  together.  Aj^parently 
stimulation  renders  the  plasma  membrane  suddenly 
permeable  to  the  osmotically  active  intracellular  sub- 
stances which  maintain  turgor.  This  elTect  is  reversible, 
and  under  normal  conditions  turgor  is  gradually  regained. 
The  leaves  of  the  Venus'  flytrap  and  the  sensitive  con- 
tractile stamens  of  the  CynarecB  show  a  behavior  essen- 
tially similar  to  that  of  Mimosa.  Temporary  loss  of 
semi-permeabihty  due  to  mechanical  stimulation  seems 
to  be  a  not  uncommon  phenomenon  in  plant  cells; 
Pfeffer  cites  the  '' stimulatory  plasmolysis''  of  diatoms 
and  other  plant  cells  as  cases  of  this  kind,  although  he 
apparently  hesitates  to  apply  this  explanation  to  the 
pulvinus  of  Mimosa} 

The  general  rules  of  stimulation  ai)])ly  U^  these 
osmotic  motor  mechanisms  of  plants,  in  the  same 
manner  as  to  the  excitation-processes  of  animal  tissues. 
Electrical  stimulation,  summation,  and  anaesthesia  occur 
under    conditions    similar    to    those    described    above, 

^Physiology  oj Plants,  English  translation,  III,  75- 


374   PROTOPLASMIC  ACIION  AND  NERVOUS  ACTION 

although  the  quantitative  relations  are  different;  hitherto 
these  relations  have  been  less  completely  investigated  in 
plants  than  in  animals.  Transmission  of  excitation  in 
plants  resembles  that  of  slowly  conducting  animal 
tissues/  and  the  excitation-process  is  accompanied  by  a 
negative  bioelectric  variation.  A  prolonged  refractory 
period  succeeds  the  motor  response  in  Mimosa,  and  this 
condition  also  appears  to  be  general  in  plants.  The 
presence  of  a  high  degree  of  turgor  in  plant  cells  renders 
the  evidence  of  a  temporary  loss  of  semi-permeability 
during  excitation  in  many  respects  more  definite  and  com- 
plete than  in  the  case  of  animal  tissues;  but  in  other  respects 
the  fundamental  processes  underlying  stimulation  appear 
to  be  of  the  same  kind  in  both  groups  of  organisms. 

In  the  higher  animals  the  phenomena  accompanying 
the  secretion  of  gland  cells,  especially  those  under  nervous 
control,  show  many  resemblances  to  those  just  described 
for  motile  plant  tissues.  There  is  the  same  loss  of  water 
and  dissolved  material  from  the  cell,  the  same  electro- 
motor variation,  and  the  same  gradual  recovery.  The 
variations  in  the  permeability  of  the  mammalian  kidney 
cells  under  the  influence  of  fear,  excitement,  or  other 
abnormal  emotional  or  nervous  conditions  also  suggest 
that  in  these  cells  stimulation  is  associated  with  increased 
permeability;  similar  evidence  is  furnished  by  sweat 
glands.  The  secretory  phenomena  accompanying  fertili- 
zation in  many  egg  cells  have  already  been  mentioned. 

It  might  be  objected  that  evidence  drawn  from  the 
observation  of  special  tissues  whose  normal  function 
consists  in  the  separation  of  dissolved  substances,  either 
formed  within  the  cells  or  collected  from  the  surround- 

^  Cf.  Bose,  Proceedings  of  the  Royal  Society,  B,  XCIII  (1922),  153. 


I 


MEMBRANE  CHANGES  DURING  STIMULATION    375 

ings,  is  scarcely  applicable  to  the  case  of  irritable  elements 
in  general.  But  such  facts  at  least  show  plainly  that 
stimulation  is  often  associated  with  increased  i)ermea- 
bility  or  other  evidence  of  temporary  structural  break- 
down; and  the  fact  that  the  conditions  under  which 
stimulation  occurs  in  other  irritable  li\ing  systems,  and 
also  its  most  general  manifestations  such  as  the  bioelectric 
variations,  are  of  the  same  kind  in  the  turgor-motor 
cells  of  plants  and  in  gland  cells  as  in  muscle  and  nerve 
points  clearly  to  the  existence  of  some  fundamental 
physico-chemical  condition  common  to  all  such  ])r()mptly 
reacting  irritable  systems.  If,  as  the  present  theory 
holds,  this  condition  consists  in  the  temporary  alteration  or 
breakdown  of  the  film-structure  which  surrounds  and  per- 
vades all  protoplasmic  systems,  the  resemblances  are  intel- 
ligible; while  in  any  case  the  differences  are  to  be  attributed 
to  special  peculiarities  of  structure  and  organization. 

The  phenomena  of  luminescence  in  animals  furnish 
additional  evidence  that  stimulation  is  associated  with 
the  temporary  breakdown  or  remo\al  of  semi-permeable 
partitions  within  the  living  system.  The  production  of 
light  in  irritable  luminescent  organisms  like  Xoctiluca 
may  be  regarded  as  an  index  of  stimulation  in  \er}'  much 
the  same  sense  as  the  bioelectric  currents  are  such 
an  index;  and  probably  both  phenomena  are  conditioned 
by  structural  changes  of  a  similar  kind.  The  investiga- 
tions of  Dubois  and  Harvey  indicate  that  in  many  if 
not  all  luminescent  animals  light-production  de])ends  on 
the  union  of  the  two  photogenic  components,  lucifcrin 
and  luciferase,  in  the  presence  of  oxygen.'     In  a  lumi- 

^  Cf.  Harvey's  recent  book,   The  Nature  of  Atiimal  Lighl  (Phila- 
delphia, 1920). 


376    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

nescent  cell  which  responds  to  stimulation  by  a  flash 
of  light,  all  three  substances  are  apparently  present  and 
available,  but  during  the  resting  state  they  are  prevented 
from  uniting  by  the  presence  of  protoplasmic  films  or 
partitions;  when  as  a  result  of  stimulation  these  parti- 
tions are  temporarily  broken  down,  chemical  union  and 
light-production  result.  Further  analysis  of  the  condi- 
tions of  luminescence  in  irritable  cells  will  no  doubt 
throw  much  light  upon  the  general  nature  of  stimulation 
processes. 

Harvey'  has  recently  made  some  simple  and  striking 
experiments  on  plant  tissues,  giving  further  indication 
that  in  living  cells  under  normal  conditions  chemical 
reactions  are  frequently  prevented  or  restricted  by  the 
presence  of  protoplasmic  partitions  or  membranes 
impermeable  to  the  interacting  substances.  The  oxidase 
reactions  which  cause  the  browning  of  potato,  apple,  or 
similar  tissues  are  examples.  If  a  potato  is  cut  in  the 
presence  of  oxygen,  the  browning  occurs  only  at  the  cut 
surface;  even  in  pure  oxygen  under  high  pressure,  the 
interior  tissue  remains  unchanged.  This  absence  of 
effect  cannot  be  referred  to  an  impermeability  to  oxygen, 
since  all  of  the  physiological  and  chemical  evidence 
indicates  that  living  protoplasm  is  freely  penetrated  by 
this  gas.  The  oxidase  and  the  chromogen  are  in  sorne 
way  prevented  from  uniting  while  the  tissue  is  Uving. 
If,  however,  it  is  exposed  for  a  few  minutes  to  chloroform 
vapor,  the  browning  extends  rapidly  throughout  the 
whole  mass.  Apparently  the  effect  of  the  chloroform 
is  to  break  down  the  protoplasmic  partitions  which 
normally  prevent  free  union  of  the  compounds.     Destruc- 

^  E.  N.  Harvey,  Jour.  Gen.  Physiol.,  V  (1922),  215. 


MEMBRANE  CHANGES  DURING  STIMl  r.ATION'    ;,77 

tion  of  semi-permeability  is  a  universal  eUect  oi  ixiisoniiiK 
with  chloroform  or  similar  substances;  this  elTcct  is  seen 
in  the  wilting  of  turgid  ]>lant  tissues,  increase  of  electrical 
conductivity,  or  diffusion  of  substances  (e.g.,  coloring 
materials)  from  the  cells.  The  leaves  of  the  common 
false  indigo  plant,  which  blacken  on  death,  also  afford  a 
striking  demonstration.'  If  the  leaves  are  poisoned  with 
chloroform  in  the  absence  of  oxygen  (e.g.,  in  a  gas 
chamber  with  hydrogen),  they  remain  green;  if  they  are 
then  exposed  to  air  they  blacken  immediately.  \\  hen 
living,  intact  leaves  are  exposed  to  oxygen  at  loo  atmos- 
pheres, no  blackening  results.  On  the  other  hand, 
mechanical  injury,  natural  death,  or  ])oisoning  all 
produce  this  effect  at  air  tension.  The  essential  condi- 
tion for  the  reaction  is  apparently  the  destruction  of 
diffusion-preventing  partitions  which  during  life  keep 
the  interacting  substances  apart.  According  to  C'hiari,'* 
autolysis  of  animal  tissues  is  similarly  hastened  by  ether 
or  chloroform.  It  thus  seems  probable  that  in  many  if 
not  all  cells  the  external  layer  of  protoplasm  (jilasma 
membrane)  is  not  the  only  semi-permeable  structure 
present,  but  that  it  is  continuous  with  a  system  of 
similarly  constituted  films  pervading  the  protoj)lasmic 
system  and  determining  the  spatial  distribution  of  the 
water-soluble  cell-constituents.^ 

If  a  temporary  breakdown  of  lilm-structure  can 
determine  chemical  effects  of  this  kind,  the  possibility 
presents  itself  that  in  cells  of  a  different  type  of  organiza- 
tion, e.g.,  muscle  cells,  other  chemical  reactions,  including 

^  Cf.  Harvey,  loc.  cit. 

^  Chiari,  Arch,  exper.  Path.  u.  PharmakoL,  LX  (1909),  256. 

3  Compare  Hofmeister's  Chcmische  Organisation  dcr  Zdle. 


378    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

those  yielding  the  energy  for  contraction,  may  be  under 
similar  kind  of  control.  In  these  cells  the  chief  reactions 
following  stimulation  probably  occur  at  the  surface  of 
the  contractile  fibrils,  and  apparently  certain  reaction- 
products,  e.g.,  lactic  acid,  are  directly  concerned  in 
the  resulting  contraction.^  We  may  assume  that  the 
temporary  breakdown  of  the  interfacial  film  (between 
fibril  and  sacroplasm)  will  have  a  double  effect:  (i) 
permit  access  of  diffusible  substances  (possibly  of  the 
lactic  acid)  to  the  interior  of  the  fibril;  and  (2)  form  the 
condition  of  a  change  of  surface-tension,  in  the  same 
general  manner  as  in  the  Hg-HaOa  system.  Under  these 
conditions  contractile  effects  (essentially  of  an  electro- 
capillary  kind)  would  result.  Hence  the  consideration 
of  the  relation  of  film-structure  to  the  chemical  reactions 
of  protoplasm  has  an  obvious  bearing  on  the  problem  of 
the  conditions  of  contractility  in  muscle  and  other  con- 
tractile tissues. 

^  For  a  discussion  of  the  part  played  by  acids  in  the  contractile 
mechanism  cf.  the  recent  review  of  A.  V.  Hill,  Physiological  Reviews,  II 
(1922),  310. 


CHAPTER  X\^ 

THE  PHYSICO-CHEMICAL  BASIS  OF  TRAX.sMlSSIOX 
IN  NERVE  AND  OTHER  PROTOPLASMIC 

SYSTEMS 

The  view  that  the  transmission  of  the  excitation- 
state  from  the  active  region  of  an  irritable  i)rot()i)hismic 
element  to  the  adjacent  resting  region  is  the  result  of 
secondary  electric  stimulation  by  the  local  bioelectric 
current  between  the  two  areas  is  one  which  is  suj)i)ortc(l 
by  general  theoretical  considerations  and  by  a  variety 
of  direct  and  indirect  evidence.  In  a  general  sense  there 
is  nothing  novel  about  this  hypothesis,  which,  like  most 
scientific  conceptions,  has  had  its  historical  background 
and  development;  it  was  expressed  tentatively  by  Du 
Bois-Reymond^  and  in  a  more  definite  form  by  Hermann;-' 
more  recently  Kiihne,  Cremer,  Gotch,  Keith  Lucas, 
and  others  have  supported  it  on  various  grounds.-'  The 
absence  in  nerv-e  of  any  observable  accompaniment  of 
the  local  excitation  process,  other  than  the  electric 
variation,  which  could  conceivably  serve  as  a  stimulus 
to  the  resting  region  adjoining  the  active  area,   is  in 

^  Gesammelle  Ahhandlungcn  zur  allgcmeincn  Muskcl  utid  Xcncn- 
physik,  II,  p.  698;  cf.  p.  733. 

2  See  especially  the  clear  statement  by  Hermann  in  his  Uiindbuch, 
II,  194,  cited  in  Cremer's  comprehensive  article  on  nerve  physiology  in 
Nagel's  Handhiich  der  Physiologic,  IV,  2d  half  (1909),  929. 

3  Kuhne,  Croonian  Lecture,  Proceedings  of  the  Royal  Society,  WAV 
(1888),  446;  Cremer,  loc.  cit.;  Gotch,  article  on  nerve  in  Schafcr's  text- 
book, cf.  pp.  458,  557  ff.;  Keith  Lucas,  Journal  of  Physiology,  XXXIX 
(1909),  207. 

379 


380   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

itself  a  strong  argument  in  its  favor.  It  is  surprising 
that  until  recently  it  has  received  relatively  little  serious 
consideration  from  physiologists,  most  of  whom  have 
been  apparently  content  to  regard  the  bioelectric  phe- 
nomena as  inessential  by-products  of  protoplasmic  action. 
The  importance  of  the  electrical  factor  in  the  phe- 
nomena of  protoplasmic  transmission  is,  however, 
clearly  recognized  in  the  ''core-conductor"  (Kernleiter) 
theory  or  theories  of  nervous  action/  This  conception 
has  as  its  basis  the  presence  of  characteristic  polarization 
effects  in  a  nerve  through  which  a  current  is  led  (by 
non-polarizable  electrodes) ;  these  effects  closely  resemble 
those  exhibited  by  a  system  consisting  of  a  simple  metallic 
wire  surrounded  by  a  sheath  or  layer  of  electrolyte 
solution.  The  resemblance  is  so  detailed,  as  regards 
the  distribution,  rate  of  development,  and  subsidence 
of  the  polarization  potentials,  that  there  can  be  little 
doubt  of  the  essential  identity  of  the  physical  conditions 
underlying  these  phenomena  in  the  two  systems.  In 
nerve  the  surface  of  the  axone  has  usually  been  regarded 
as  the  chief  seat  of  the  polarization,  and  Hermann 
especially  has  called  attention  to  the  intimate  relations 
existing  between  polarization  and  stimulation.  Neither 
he  nor  his  successors,  however,  could  explain  satis- 
factorily, on  the  basis  of  the  phenomena  shown  by  simple 
polarization  models  of  this  type,  the  characteristic  wave- 
like transmission  of  the  electrical  variation  in  the  excited 
nerve.  Apparently  the  presence  of  special  physiological 
factors  must  be  assumed,  whose  effects  are  superposed 
on  those  of  the  purely  physical  factors.     This  point  of 

^  Cf.  Cremer's  [article,  op.  ciL,  p.  904,  for  historical  account  and 
discussion. 


PHYSICO-CHEMICAL  BASIS  OF. TRANSMISSION    3^)1 

view  has  more  recently  been  cm])hasizccl  by  Cremer  in  an 
important  series  of  studies  on  the  '' Kernlcilfr"  thcon-, 
published  at  intervals  since  1899.  ^^^  assumes  in  ners'c, 
in  addition  to  the  physical  polarization  which  this  tissue 
exhibits  in  common  with  artificial  systems  of  the  core- 
conductor  type,  the  presence  of  a  special  "physioloj^'ical 
polarization,'"  by  which  term  he  means  some  active 
process  (in  the  nature  of  a  response  or  reaction )  exhibited 
at  the  regions  of  entrance  and  exit  of  the  current;  this 
process  he  conceives  as  based  on  a  chemical  change  of 
some  kind,  which  secondarily  may  alter  polarization  and 
hence  serve  as  the  source  of  a  current.  In  this  manner 
the  polarization  effect  may  be  renewed  at  successive 
areas  of  a  nerve,  and  transmission  to  an  indefinite 
distance  becomes  possible.^ 

In  the  foregoing  form  the  Kernleiter  theory  rccjuircs 
only  slight  modification  in  order  to  make  it  entirely 
consistent  with  the  present  form  of  the  "membrane'' 
theory.  Both  theories  agree  that  a  change  ol  ])olari/a- 
tion  is  the  critical  or  primary  event  in  the  local  stimuhi- 
tion  process.  Evidently  if  the  polarization  is  confined 
to  the  surface  of  the  protoplasmic  element  (as  also  of  the 
metal  in  a  core-conductor),  this  critical  change  is  a 
surface  change.  According  to  the  membrane  theory,  the 
variation  of  polarization  in  stimulation  is  the  result 
of  a  sudden  change  in  those  features  of  structure,  comjio- 
sition,  or  permeability  which  determine  the  normal 
electromotor  properties  of  the  protoi)lasmic  surface-film 
or  plasma  membrane.     Such  a  change  may  result  from 

^  Sltzimgsber.  Ges.  Morph.  u.  Physiol.,  Munch'-n  riSoo-iooo^, 
Hefte  I  and  2. 

*See  Cremer's  exposition  in  his  article  in  Xagcl's  Hatuibuch,  p)p. 
930  ff. 


382    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

a  chemical  change  in  the  substance  of  the  membrane; 
the  theory  further  assumes  that  this  change  is  of  such  a 
kind  as  to  be  readily  induced  by  the  passage  of  a  current. 

The  analogy  between  this  hypothetical  type  of 
process  and  the  phenomenon  known  as  ''local  action"  at 
metallic  surfaces  is  a  close  one,  to  which  I  have  recently 
called  attention/  An  example  is  the  spread  of  corrosion 
in  metals  like  iron  in  contact  with  electrolyte  solutions; 
this  spread  is  the  result  of  local  chemical  action  under  the 
influence  of  local  electrical  circuits  between  the  altered 
and  the  unaltered  areas  of  the  metal.  The  possibility 
is  thus  suggested  that  in  the  irritable  protoplasmic 
element  the  primary  change  in  electrical  excitation  is 
also  of  the  nature  of  an  electrolysis.  Through  the 
chemical  change  thus  induced  the  properties  of  the 
surface-film  are  altered  in  such  a  manner  as  to  render  it 
^'negative"  to  unaltered  areas;  a  local  circuit  then 
arises  at  the  boundary  between  altered  and  unaltered 
areas  and  causes  electrolysis  in  the  latter,  in  the  same 
manner  as  the  original  current;  and  by  a  repetition  of 
this  effect  the  chemical  and  electromotor  change  spreads. 
Evidently  a  wavelike  transmission  without  decrement 
is  theoretically  possible  under  these  conditions.  The 
chief  requirement  is  the  presence  of  a  uniform  and 
chemically  unstable  film  forming  the  boundary  layer 
of  the  irritable  element. 

Conditions  of  essentially  this  kind  are  in  fact  realized 
in  the  passive  iron  wire  in  nitric  acid  solution;  and  in 
this  simple  inorganic  system  the  phenomena  of  activation 
and  transmission  exhibit  a  surprisingly  detailed  resem- 

'"  Electrolytic  Local  Action  as  the  Basis  of  Propagation  of  the 
Excitation- Wave,"  American  Journal  of  Physiology,  XLI  (191 6),  126. 


PHYSICO-CHEMICAL  BASIS  OF  TRAXSMISSION    383 

blance  to  those  observed  in  ncr\e  and  ollu-r  condiutinK 
protoplasmic  systems.  The  possibility  of  transmissions 
of  the  general  type  above  is  thus  demonstratcfl.  and  the 
problem  becomes  chiefly  one  of  determinin<r  the  spcdal 
nature  of  the  conditions  present  in  the  li\ing  system. 
It  is  obvious  that  polarization  elTccts  are  ])rcscnt  at 
the  surface  of  the  iron  wire  when  a  current  is  passc<i 
through  the  system,  just  as  in  the  case  of  the  phitinum 
wire  in  the  core-conductor  experiments  of  Hermann, 
Matteucci,  and  Boruttau.  Changes  of  polarization, 
however,  can  give  rise  to  unlimited  transmission  only 
in  so  far  as  they  form  the  condition  of  chemical  effects 
which  alter  the  electromotor  properties  of  the  surface 
layer  and  themselves  cause  further  changes  of  polariza- 
tion. The  general  conditions  of  transmission  in  proto- 
plasmic systems  will  now  be  discussed  brietly,  with  more 
particular  reference  to  the  case  of  ners'e,  where  the 
phenomena  of  protoplasmic  transmission  a])])car  to 
exhibit  themselves  under  the  simplest  conditions.  The 
fundamental  problem,  however,  is  the  same  for  all  forms 
of  protoplasm. 

According  to  the  law  of  polar  stimulation,  the  direc- 
tion of  the  current  between  active  and  resting  areas  is 
such,  relatively  to  the  surface  of  the  irritable  clement, 
that  its  normal  physiological  effects— assuming  them  to 
be  the  same  as  those  of  an  external  current  led  into  the 
tissue — would  be  to  initiate  excitation  at  the  resting 
region  adjoining  the  excited  area  and  to  repress  activity 
in  the  excited  area  itself.  An  inspection  of  the  diagram 
(Fig.  4)  will  show  this.  The  direction  of  the  local  bio- 
electric current  (relatively  to  the  protoplasmic  surface) 
at  R  is  the  same  as  that  of  the  external  currmt  at  the 


384   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

cathode  of  a  pair  of  stimulating  electrodes.  A  current 
traversing  the  protoplasmic  surface  in  this  direction  arises 
as  soon  as  the  local  area  of  stimulation,  S,  is  altered 
(e.g.,  by  mechanical  or  chemical  action)  sufficiently  to 
render  it  negative  relatively  to  the  areas  adjoining. 
The  appearance  of  this  current,  which  acts  at  a  distance 
from  the  directly  altered  area,  is  apparently  the  primary 
effect  in  stimulation.  It  initiates  the  propagated  wave- 
like disturbance,  because   each  secondarily  stimulated 


5 


Fig.  4. — In  A  the  arrows  represent  the  direction  of  the  current  in  the  active-inactive 
circuit  on  one  side  of  the  stimulated  region  S.  In  B  the  course  of  an  external  stimulating 
current  from  a  battery  is  represented.  Stimulation  originates,  on  make,  at  the  cathodal 
region,  where  the  current  has  the  same  direction,  relatively  to  the  membrane,  as  at  R. 

area,  e.g.,  at  region  R,  on  itself  becoming  negative, 
produces  automatically  the  same  effect  on  regions 
beyond;  and  this  effect  is  repeated  at  each  boundary 
(or  region  of  transition)  between  an  active  area  and  the 
resting  area  in  immediate  advance  of  it. 

There  is  an  analogy  of  a  general  kind  between  the 
spread  of  excitation  over  an  irritable  protoplasmic 
element  and  the  spread  of  combustion  along  a  fuse, 
with  the  difference  that  in  the  fuse  the  chemically 
active  area  initiates  action  in  the  adjoining  area  through 
the  heat  generated  in  the  local  reaction,  while  in  the 


PHYSICO-CHEMICAL  BASIS  OF  TI<.\XSMISSIO\     ^85 

protoplasmic  element  transmission  is  ctk-ctccl  by  the 
electric  current  flowing  between  the  two  adjacent  areas 
of  different  potential.  In  the  fuse  a  temperature  grach'ent 
exists  between  the  burning  area  and  the  region  adjoining, 
and  the  reaction  begins  wherever  the  tem])erature  rca(  hes 
the  ignition  point.  The  rate  of  transmission  in  such  a 
case  depends  on  the  maximal  distance  (from  the  l>oundary 
of  the  burning  area)  at  which  this  critical  temi)eraturc  is 
reached  and  on  the  rate  at  which  heat  is  locally  developed; 
i.e.,  V  =  Ksr  where  V  is  the  speed  of  transmis>ion,  s 
the  maximal  distance,  and  r  the  rate  at  which  temperature 
rises  in  the  ignited  area.'  Simihirly  in  the  ner\-e  a.xone 
(or  other  protoplasmic  element)  the  velocity  of  transmis- 
sion will  be  a  direct  function  (i)  of  the  maximal  distance, 
^  (from  the  active  area)  at  which  the  current  of  the 
local  bioelectric  circuit  is  effective  as  stimulus,  and  (2) 
of  the  rate,  r,  at  which  the  current  devel()])s;  a'jain 
V  =  Ksr.  Instead  of  the  rate  of  development,  r,  we 
may  consider  its  reciprocal,  the  time,  /,  required  for  the 
current  at  the  secondarily  stimulated  point  at  distance, 
s,  to  attain  a  stimulating  value;  the  shorter  this  time 
the  more  rapid  the  transmission,  i.e.,  V  =  Ks/L' 

This  equation  also  applies  to  the  transmission  in  the 
passive  iron  model.  Between  the  activated  and  the 
inactive  areas  of  an  iron  wire  immersed  in  dihite  nitric 

^K  represents  constant  limiting  factors,  such  as  tlic  rate  at  which 
heat  is  conducted  or  radiated  from  the  burning  region. 

The  distribution  of  temperature  in  the  gradient  on  cither  side  of  a 
heated  area  in  a  wire  (or  similar  heat-conductor)  is  in  fact  subject  to 
the  same  quantitative  law  as  the  distribution  of  i>olcnli.il  in  a  ItK-ally 
polarized  core-conductor,  as  Cremer  has  pointed  out  (<)/>.  cil.,  pp.  906  ff.). 

2  For  a  fuller  discussion  cf.  my  article  in  .1  mcrican  Jouniat  of  Pkys- 
iology,  XXXIV  (1914),  414;  cf.  pp.  43^'  ff-;  -^J^"  ''"'''•'  X>^XV^I  (JQIS). 
362  jBf.     Cremer  has  recently  derived  a  more  detailed  fonnuU  for  the 


386    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

acid  there  is  a  P.D.  of  about  0.7  volt;  a  local  current 
flows  between  the  two  areas  as  indicated  in  Figure  3 
(p.  253),  the  active  area  being  anodal/  This  current  is 
most  intense  near  the  active-passive  boundary,  because 
the  resistance  of  the  portion  of  current  traversing  the 
surface  at  any  point  in  the  passive  area  increases  with 
the  distance  of  that  point  beyond  the  boundary;  this 
resistance  depends  chiefly  on  the  length  and  specific 
conductivity  of  the  column  of  electrolyte  intervening. 
Up  to  a  certain  critical  distance,  s,  beyond  the  boundary 
the  current  wfll  have  sufficient  intensity  and  local 
density  to  reduce  the  film;  hence  the  time,  /,  required 
for  the  current  to  reach  this  intensity  and  the  distance, 
s,  from  the  boundary  are  the  essential  variables  to  be 
considered.^  The  effect  of  increasing  the  resistance  of 
the  local  circuit  (and  thus  decreasing  the  distance,  s) 
may  be  shown  quaUtatively  by  suspending  the  passive 
wire  vertically,  with  a  thin  layer  of  acid  adhering,  and 
then  touching  it  below  with  zinc.^     Under  these  condi- 


velocity  of  transmission  in  nerve,  introducing  as  factors  the  relative 
electrical  resistances  of  axone  and  sheath  and  the  specific  electrical 
sensitivity  of  the  tissue,  as  well  as  the  rate  of  development  of  the  electric 
variation.  If  certain  reasonable  assumptions  are  made,  this  formula 
agrees  well  with  observation.  Cremer's  formula  is  consistent  with  the 
foregoing  sunpler  expression,  V  =  Ks/t,  but  attempts  to  define  more 
closely  the  conditions  determining  the  value  of  5  (Ber.  ges.  Physiol.,  II 
[1920],  166;  also  Cremer's  Beitrdge  zur  Physiologic,  II  [1922],  Heft  i,  31). 

*  Jour.  Gen.  Physiol.,  Ill  (1920),  130. 

'  Only  the  maximal  distance  from  the  boundary  at  which  the  current 
is  effective  need  be  considered,  since  both  systems  react  in  the  "all 
or  none"  manner.  This  type  of  reaction  is  a  necessary  condition  for 
indefinite  transmission  without  decrement. 

3  It  may  also  be  shown  quantitatively  by  inclosing  the  wires  in  glass 
tubes  of  different  diameters;  the  rate  varies  directly  with  the  sectional 
area  of  the  tube. 


PHYSICO-CHE.AIICAL  BASIS  OF  TRANSMISSION     387 

tions  the  wave   of  activation  fman.cd  by  tlu-  .  i- 

ing  of  the  metanic  surface)  moves  slowly  upward  at 
the  rate  of  only  a  few  centimeters  per  second;  whUc 
in  the  case  of  a  wire  completely  immersed  in  a 
large  volume  of  acid  the  transmission  is  too  rapid  to 
follow  with  the  eye,  i.e.,  some  hundred  cenlii  |)cr 

second. 

Rapidity  in  the  local  variation  of  potential  in  nerve 
or  other  conducting  tissue  is  thus  a  necessary  condition 
for  rapidity  of  transmission.  The  table  given  on  page 
328  shows  a  general  proportionality  between  the  rate 
of  development  of  the  bioelectric  currents  in  d.  it 
tissues  and  the  rate  of  transmission.  Tiie  slowing  of 
the  bioelectric  variation  in  a  particular  tissue,  by  cold, 
anaesthesia,  or  fatigue,  invohcs  a  corresponding  slowing 
in  the  transmission  rate.  An  exact  proportionality  is 
hardly  to  be  expected,  because  the  other  })roperties  of 
the  tissue,  especially  its  irritability  and  its  electrical 
conductivity,  are  also  affected  by  the  change  of  condi- 
tions, and  other  variables  enter;  but  that  the  rate  of 
electromotor  variation  is  the  chief  factor  determining 
the  speed  of  transmission  seems  clearly  indicated  by  tiie 
observations  cited  in  the  table. 

With  regard  to  the  other  variable,  s,  the  di  c 

from  the  active-resting  boundary  through  which  the 
local  bioelectric  current  is  effective  as  a  stimulus,  detinitc 
information  is  difficult   to  obtain.     T   have  att<  \ 

to  estimate  this  distance  in  frogs'  nerve  by  i  g 

the  maximal  distance  between  two  platinum  *.'.  s, 

applied  to  the  tissue  and  having  a  IM).  similar  lo 
that  of  the  bioelectric  variation  (20  to  40  millivolts), 
at  which  stimulation  occurs  on  the  make  and  break  of  a 


388    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

constant  current.^  With  a  P.D.  of  ten  to  twenty 
millivolts,  stimulation  occurs  at  either  make  or  break 
with  the  electrodes  fifteen  to  twenty  milhmeters  apart. 
If  we  regard  the  conditions  of  resistance  as  similar  in  a 
stimulating  circuit  of  this  kind  and  in  the  normal  bio- 
electric circuit,  we  may  infer  that  the  normal  action- 
current  flowing  between  the  active  and  the  resting 
portions  of  an  excited  nerve  is  effective  at  a  distance  of 
three  to  four  centimeters  from  the  excited  area.  Other 
observations,  by  Hering  and  others,  on  secondary 
stimulation  by  the  demarcation-current,  support  this 
conclusion.^ 

The  local  action-current  in  the  frog's  motor  nerve 
reaches  its  maximum  at  about  .001  of  a  second  after 
its  initiation  (at  20°);  this  is  the  duration  of  the  rising 
phase  of  the  action-current  curve,  according  to  the 
observations  of  Garten  and  others.^  If  we  assume  that 
this  current,  at  the  moment  of  reaching  its  maximum, 
has  a  stimulating  effect  on  all  resting  regions  of  the  nerve 
within  a  distance  of  three  centimeters  from  the  active 

^  Op.  cit.  (1914),  p.  433- 

'  Cf.  article  just  cited,  p.  431.  See  also  the  recent  observations  of 
Spierling  (Cremer's  Beitrage  zur  Physiologie,  I  [1918],  Heft  7)  and  Keil 
(Z.  fur  Biologic,  LXXV  [1922],  i),  on  the  minimal  P.D.  required  for 
the  stimulation  of  frog's  nerves.  In  Keil's  experiments  electrodes  of 
varying  form  were  used,  and  the  stretch  of  nerve  traversed  by  the  current 
varied  between  0.5  and  4  cm.  in  length.  The  values  obtained  were  of 
a  similar  order  to  those  found  in  my  experiments  just  cited,  but  showed 
wide  variation.  The  potentials  required  with  stretches  of  nerve  2  to  4 
cm.   long  varied   between    20  and   ca.   300  millivolts. 

3  More  recent  determinations  indicate  a  more  rapid  rise;  cf.  Gasser 
and  Erlanger's  observations  with  the  cathode  ray  oscillograph  {American 
Journal  Physiology,  LXII  [1922],  496;  also  Plant,  Z.  fUr  Biol.,  LXXVIII 

([1923].  133)- 


PHYSICO-CHE.MK  \I.  BASIS  OF  TRAXSMIssK  ,.n      ^  ^^^ 

area,  we  have  a  transmission  of  slinuilalin^;  c! 
through  three  centimeters  in  .001  of  a  sccon<l 
equivalent  to  thirty  meters  per  Miond,  ihc  usual 
transmission- velocity  at  tliis  temperature.  The  rcsulli 
of  this  simple  calculation  are  thus  in  agreement  with 
observation  and  support  the  view  that  transr  "  '  11  is  in 
reality  a  case  of  secondary  stimulation  by  tlu-  cuf 


TTTTr^W^ 


> 


Fig.  5. — Diagram  of  the  momentary  conditions  in  a  -« 

at  20°.     The  shaded  region  markeci  A,  between  /fj  and  K,.  ;  I 

under  consideration  by  the  excitation-wave,  which  is  rcgardctl  as  ..  v 

tion  of  the  large  arrow  at  the  rate  of  30  meters  per  second.  It>  Icnicth,  ■Mumint  tfat 
total  duration  of  the  local  process  (as  indicated  by  the  dumlidn  nf  the  local  biockctric 
variation)  to  be  .cx>2  second,  is  0  cm.     The  excitation-priKos  is  just  berinnini  sT  *,. 

has  reached  its  maximum  at  A 10,  and  has  just  subsided  at  Rt.    The  curvr  4 

variation  from  the  resting  potential  at  different  points  in  the  activt  n 
P.D.,  at  Aio,  is  ca.  40  millivolts.     The  regions  marked  K  arr  •• 
small  arrows  indicate  the  direction  of  the  bioelectric  current 
tion  of  the  active-resting  circuit.     Between  R,  and  R,  ila  intensity  it 

the  nerve;    excitation  is  thus  always  being  initiate*!  at    •.  4 

the  wave  front  (i.e.,  up  to  R,).     For  a  somewhat  simiUr  i!. « 

excitation-wave  the  nerve  is  refractory  to  stimulation. 

of  the  local  bioelectric  circuit.  Fi«;urc  5  p;\ves  a  diagram- 
matic representation  of  the  conditions  in  a  nerve  during 
transmission. 

The  course  of  the  current  in  the  bioelectric  circuit 
should  be  noted;  this  course  is  partly  cxtra-ccllular, 
i.e.,    through    the    medium,'    and   j)artly   inlra-ccllular, 

»  Part  of  this  current  passes  throuRh  the  galvanomrtrr  »hrn  ihc 
action-current  is  recorded  by  such  an  instrument,  the  rcn  »ugh 

the  medium  or  other  extracelluhir  conducting  |>alh. 


390   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

the  current  at  its  regions  of  entrance  and  exit  also 
traverses  the  plasma  membrane.  The  current  passing 
lengthwise  along  the  fibers  of  a  tissue  like  a  nerve  is 
undoubtedly  subject  to  electrostatic  retardation,  as  in 
the  analogous  case  of  a  cable;  and  Crehore  and  Williams^ 
have  calculated  that  the  speed  with  which  its  variations 
are  transmitted  would  thus  be  reduced  to  a  value  similar 
to  that  of  the  nerve  impulse.  It  is  evident  that  an  upper 
limit  to  the  speed  attainable  by  transmission  of  the  kind 
above  is  set  by  the  speed  with  which  variations  of  current- 
intensity  can  be  transmitted  lengthwise  along  such  a 
conductor,  since  the  general  physical  conditions  present 
in  conductors  with  boundary  surfaces  having  capacity 
are  undoubtedly  present  in  protoplasmic  structures  like 
nerves.  Such  conditions  are  common  to  all  conducting 
paths  having  a  certain  structure  (core-conductors). 
It  would  be  erroneous,  however,  to  infer  that  trans- 
mission in  nerve  is  identical  with  transmission  along  a 
cable.  The  nerve  impulse,  or  any  other  protoplasmic 
excitation-wave,  is  an  active  process  whose  energy  is 
derived  at  each  portion  of  its  path  from  local  chemical 
reactions.  Its  electrical  component  furnishes  the  condi- 
tions for  transmission  from  each  region  to  the  next, 
but  does  not  constitute  the  whole  process  in  the  physi- 
ological sense.  Nevertheless  the  conclusion  that  certain 
physical  factors  are  common  to  both  systems  must  on 
general  scientific  grounds  be  regarded  as  correct. 

Since  a  portion  ('' return  path")  of  the  bioelectric 
current  traverses  the  external  medium,  we  should  expect 
that  varying  the  electrical  conductivity  of  the  medium 

^  Crehore  and  Williams,  Proceedings  of  the  Society  of  Experimental 
Biology  and  Medicine,  XI  (1913),  59. 


PHYSICO-CHEJMICAL  BASIS  OF  TR  WSAU^ION    391 

would  have  a  correspond in.t;  ciTcct  upon  ihc  speed  ui 
protoplasmic  transmission.  A  lowering  of  the  conduc- 
tivity of  the  local  bioelectric  circuit  should  involve  a 
corresponding  decrease  in  this  velocity,  since  the  n:  d 

distance,  s,  at  which  the  local  current  still  has  stim  .  g 
intensity,  would  l^e  i)roj)ortionately  decreased  by  any 
increase  of  electrical  resistance.  This  critical  distance 
should,  other  conditions  bein^  equal,  be  projM)rlional 
to  the  conductivity  of  the  circuit.  Mayor's  exiK'rimcnls 
on  the  rate  of  transmission  in  the  nerve  net  of  the 
medusa  Cassiopea  in  dilute  sea  water  show  in  fact  that 
within  a  considerable  range  of  dilutions  (down  to  50 
volumes  per  cent  sea  water)  a  close  proportionality 
exists  between  the  salt-content  of  the  medium  and  the 
transmission  rate.'  This  result  indicates  a  direct 
correlation  of  this  rate  with  the  electrical  conductivity 
of  the  medium.  The  recent  investigation  of  Pond'  on 
the  speed  of  the  contraction-wave  in  various  forms  of 
muscle  (cardiac  and  voluntary  of  frog  and  heart  of 
Limiih(s),  using  mixtures  of  balanced  Sidt  solution  and 
isotonic  sugar  solution,  has  shown  that  in  these  tiivsues 
also  the  speed  of  transnu'ssion  runs  closely  parallel 
wdth  the  electrical  conductivity  of  the  medium.  The 
transfer  of  a  muscle  from  a  medium  of  low  to  one  ^^ 
high  conductivity  is  followed  by  a  corresponding  incri  .i^ 
in  the  speed  of  the  contraction-wave,  and  vice  vt 
Mayor's  and  Pond's  observations  are  dithcult  to  <  a 

except  on  the  assumption  that  electric  currents  tra^ 
the  cell-media  are  a  chief  factor  determining  thr  mtr  nt 

'  A.  G.  Mayor,  AmcrUan  Journal  oj  V  gy,  XI-Il 

andXLIV,  591. 

'  S.  E.  Pond,  Jour.  Gen.  Physiol.,  Ill  (192 1)  S07. 


392  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

which  excitation  is  transmitted  from  one  region  of  a 
protoplasmic  element  to  another;  this  assumption, 
however,  is  a  direct  corollary  of  the  local  action  theory 
of  transmission.  Further  comparative  observations  in 
this  field  are  desirable;  the  theoretical  side  also  needs 
careful  consideration,  since  both  extracellular  and 
intracellular  conductivities  are  concerned  and  the 
precise  relations  between  these  two  are  insufficiently 
known/ 

Various  other  facts  of  comparative  physiology  also 
indicate  the  importance  of  the  bioelectric  variations  in 
the  different  forms  of  protoplasmic  transmission.  The 
transmission  of  excitation  between  cells  which  are  in 
contact  or  close  proximity  but  not  otherwise  connected 
is  a  phenomenon  difficult  to  explain  except  on  the  electri- 
cal theory;  the  ^'rheoscopic  frog"  experiments  have 
already  been  cited  as  examples  of  transmission  demon- 
strably resulting  from  secondary  electric  stimulation  by 
bioelectric  currents.  Several  years  ago,  I  called  atten- 
tion to  a  number  of  instances  of  apparently  the  same 
effect;^  for  example,  one  active  swimming  plate  in  a 
ctenophore  can  influence  another  through  several 
millimeters  of  sea  water;  spermatozoa  collected  in  a 
clump  are  soon  found  beating  synchronously;^  ciliated 
epithelial  cells  transmit  waves  of  movement;   the  trans- 

^  Brooks  has  recently  studied  the  relation  between  the  conductance 
of  living  cells  and  tissues  {L'aminaria,  yeast,  bacteria,  Chlorella)  and  the 
conductivity  of  the  medium,  and  finds  a  close  proportionality  between 
the  two  {Jour.  Gen.  Physiol.,  V  [1923],  365. 

2  Op.  cit.  (1914),  pp.  427  ff. 

3  The  detached  cilia  of  Paramoecium  show  a  similar  behavior, 
according  to  recent  obsrvations  of  Al  verdes  {Arch.  ges.  Physiol.,  CXCV 
[1922],  245). 


PHYSICO-CHEIMICAL  BASIS  OF  TRANSMISSION    393 

missions  between  neurones  in  the  central  nervous 
system  and  between  nerve-endings  and  muscle  cells 
are  evidently  by  contact.  Such  transmissions  point 
almost  certainly  to  electrical  conditions.  The  sensitivity 
of  certain  irritable  elements  to  electrical  currents  in  the 
surroundings  has  in  some  cases  been  developed  to  a 
remarkable  degree;  for  example,  the  catfish  will  respond 
to  the  dipping  of  a  metallic  rod  into  the  aquarium  at  a 
distance  of  several  centimeters  from  the  fish.*  It  is 
possible  that  such  animals  may  detect  living  prey 
through  the  action-currents  accompanying  muscular 
movements. 

Transmission  of  excitation  or  other  physiological 
influence — implying  transmission  of  chemical  influence 
to  a  distance  in  protoplasm— may  be  callcHl  "physi- 
ological distance-action,"  after  the  analog)'  of  ''chemical 
distance-action";  the  latter  is  an  electrical  phenomenon 
depending  on  the  mutual  influence  of  the  electrode 
areas  in  circuits.^  A  simple  example  will  illustrate. ■* 
WTien  a  copper  or  platinum  wire,  e.g.,  25  centimeters 
long,  is  immersed  in  a  vessel  of  dilute  H^SO^  and  touched 
at  one  point  with  a  piece  of  zinc,  instantly  bubbles  of 
hydrogen  start  out  from  the  surface  of  the  wire  along 
its  entire  length.  The  zinc  forms  the  anode  in  the  local 
circuit  produced  by  the  contact,  the  copper  or  |)latinum 
is  the  cathode,  hence  hydrogen  is  formed  from  the  surface 
of  the  latter  at  all  points  where  the  current-intensity  is 

»  Parker  and  von  Hcuscn,  American  Journal  of  Physiology,  XLIV 
(1917),  405 

'Cf.  Ostwald,  "Chemischc  Fcrncwirkung."  /.  physik.  Chem  ,  IX 
(1891),  540. 

3  For  other  similar  instances  and  a  fuller  discussion  of  the  biological 
analogies  cf.  Biological  Bulletin,  XXXIII  (1917),  155-   cf.  pp.  iS7  ^- 


394   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

sufficient.  In  other  words,  a  reducing  action  comes 
instantly  into  play  at  a  distance  from  the  zinc  as  soon 
as  the  contact  is  made;  this  action  depends  on  the  passage 
of  the  current  through  the  circuit,  zinc,  acid,  and  plati- 
num. Similarly  when  a  region  of  nerve  is  stimulated, 
that  region  becomes  negative;  and  the  presumption  is 
that  the  current  of  the  local  circuit  thus  arising  exerts 
chemical  action  at  all  points  along  the  protoplasmic 
surface  where  its  intensity  is  sufficient.  According  to 
the  present  theory,  it  is  to  this  electrochemical  action 
(which  secondarily  deterinines  stimulation)  that  the 
transmission  is  due.  Each  area  thus  secondarily  activ- 
ated serves  as  a  new  point  of  departure  for  activation 
of  the  region  beyond,  and  in  this  manner  transmission 
to  an  indefinite  distance  becomes  possible.  As  already 
pointed  out,  the  conditions  in  the  passive  iron  model 
are  of  the  same  general  nature.  The  electrochemical 
modification  of  the  surface  layer  (plasma  membrane  or 
passivating  oxide  film) ,  through  the  electrolytic  action  of 
the  local  circuit,  is  in  both  systems  the  essential  change 
determining  transmission. 

In  the  return  to  the  resting  or  passive  state  after 
activation  the  current  of  the  local  circuit  is  also  an 
essential  factor;  this  current  (as  the  diagram  shows) 
passes  in  opposite  directions  (relatively  to  the  surface) 
at  active  and  resting  regions;  and  correspondingly  its 
physiological  effect,  which  is  excitatory  at  the  resting 
region  adjoining  the  region  of  activity,  is  anti-excitatory 
or  inhibitory  at  the  active  region  itself.  Any  region,  on 
becoming  active,  is  thus  automatically  subjected  to  an 
electrical  influence  which  Kmits  or  arrests  its  activity. 
Hence  the  local  activity,  in  a  muscle  cell  or  nerve  fiber, 


PHYSICO-CHEJMICAL  BASIS  OF  TRANSMISSION    395 

is  temporary,  and  the  state  of  excitation  appears  to 
travel  like  a  wave  over  the  irritable  element. 

In  the  wire  model  the  automatic  return  of  passivity 
in  strong  HNO3  is  the  direct  result  of  the  formation  of  a 
new  surface-film  by  electrochemical  (oxidative)  action 
at  the  local  anodal  regions.'  The  phenomena  of  the 
refractory  period  in  irritable  tissues,  and  the  observations 
already  described  showing  that  the  plasma  mcml)ranc 
of  egg  cells  changes  from  a  temporarily  unstable  to  a 
stable  state  after  cell-division  or  insemination.^  indicate 
that  in  living  irritable  elements  also  the  essential  condi- 
tion of  recovery  after  stimulation  is  the  formation  of  a 
new  surface-film,  or  the  return  of  the  altered  film  to  its 
original  condition.  Other  physiological  facts  support 
this  view;  e.g.,  the  delay  in  the  return  of  irritability 
in  a  veratrinized  muscle  after  stimulation  is  associated 
with  a  corresponding  delay  in  the  return  phase  of  the 
bioelectric  variation.  The  reversible  change  in  the 
surface-film  is  the  condition  both  of  the  normal  bioelectric 
variation  at  any  region  and  of  the  transmission  of  a 
similar  change  of  state  to  adjoining  regions. 

The  well-known  interference  with  stimulatiuu  ami 
transmission  during  the  passage  of  a  constant  current 
lengthwise  through  a  muscle  or  nerve  is  a  further  indica- 
tion of  the  part  played  by  electrical  conditions  in  trans- 
mission. The  region  near  the  anode  (region  of  an- 
electrotonus)  acts  as  a  block  to  an  excitation-wave; 
this  effect  is  undoubtedly  complex,  but  it  is  probable 

^  For  a  fuller  account  of  the  conditions  in  passive  n^-  ♦  •'-  cf.  the 

review  of  Bennett  and  Burnham,  Journal  of  Physical  CL ^,  XXI 

(1917),  107. 

2  Cf.  pp.  361  flf. 


396    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

that  it  depends  largely  upon  the  direct  physical  com- 
pensation of  the  bioelectric  current  of  the  approaching 
excitation-wave,  which  in  the  region  beyond  the  actual 
area  of  excitation  traverses  the  surface  in  a  direction 
opposed  to  that  of  the  polarizing  current  (Fig.  6). 
An  analogous  effect  is  observed  in  a  passive  iron  wire 
in  nitric  acid  when  a  piece  of  platinum  foil  is  pressed 
into  close  contact  with  it;    an  activation  wave  started 


^^_jj2:  ^^ 


cuielactro 
tonic,  regmn. 


cuctii/e.  ~  inaciiue.  pola.yi'zing' 

circut't  ef- e.xcita:Cion.-iA/aM&  o^cuit- 

Fig.  6. — Showing  the  opposed  directions  of  action  current  and  polarizing  current 
through  the  resting  portion  of  the  nerve  in  the  anelectro tonic  region;  the  excitation 
wave  is  nearing  the  anodal  region  of  a  battery  current  led  into  the  nerve  by  non-polarizable 
electrodes. 

at  another  region  of  the  wire  is  blocked  in  the  vicinity 
of  the  platinum.  This  effect  is  dependent  on  the 
intersection  of  the  two  local  circuits,  active-passive  and 
platinum-passive,  which  are  opposed  in  direction. 

The  mutual  interference  of  excitation- waves  in  living 
tissues  is  probably  to  be  explained  in  an  essentially 
similar  manner  as  an  instance  of  mutual  compensation 
of  oppositely  oriented  bioelectric  circuits.  This  phe- 
nomenon is  best  demonstrated  in  rings  of  medusa 
tissue^  or  rings  of  heart  muscle;''  two  con  traction- waves 

^  Cf.  A.  G.  Mayor,  Carnegie  Institute  Publicatiotis,  No.  102  (1908), 
p.   115;    American   Journal  of  Physiology,  XXXIX    (1916),   375;    cf. 

p.  379- 

^W.  E.  Carrey,  American  Journal  of  Physiology,  XXXIII  (1914), 
409. 


PHYSICO-CHEMIC\L  BASIS  OF    TRANSMISSION-     ^g; 

approaching  each  other  from  ()])j)osilc  directions  undcr^^. 
mutual  extinction  where  they  meet.  It  is  clear  that 
the  processes  determining  transmission  arc  in  some 
manner  compensated  or  nullified  where  the  waves  meet; 
and  since  each  wave  is  associated  with  a  hioclectric 
circuit,  and  the  two  circuits,  being  equal  and  oppositely 
oriented,  must  physically  compensate  each  other  when 
superimposed,  it  is  to  be  expected  that  any  transmission 
of  electric  influence  and  hence  of  stimulating  elYect 
beyond  their  intersection  will  be  imi)ossible.  The  block- 
ing of  excitation-waves  at  regions  of  injury  is  probably 
to  be  explained  in  a  similar  manner,  as  due  to  comj)ensa- 
tion  of  the  action  current  by  the  injury  current.' 

The  question  of  the  part  which  interferences  of  thi> 
kind  play  in  the  intact  living  organism  (e.g.,  in  the 
central  nervous  system)  is  an  open  one.  Recently 
there  have  been  attempts  to  ex])lain  j)hysiological 
interferences  such  as  those  of  reciprocal  inhibition,  the 
Wedensky  phenomenon,  vagus  inhibition,  etc.,  on  the 
basis  of  a  lack  of  correspondence  between  the  normal 
rhythm  of  response  and  recovery  in  the  recei\ing  irritable 
system  and  the  rhythm  of  the  series  of  nervous  impulses 
entering  it  from  without.-  The  Wedensky  elYect  is  an 
example  of  such  a  phenomenon,  the  failure  of  the  muscle 
to  respond  after  the  initial  contraction  depending  on 
the  coincidence  of  ])eriods  of  increased  tlecrement  in 
the  motor  end-plate    with    the    jieriods    at    which   the 

'  Mayor  refers  the  mutual  extinction  of  intersecting  waves  to  the 
refractory  phase  of  the  tissue;    "tissue  which  has  been  in  . 
cannot  again  contract  until  after  an  appreciable  interval  of  rcsL  '     1.. 
trical  compensation  must,  however,  also  be  present,  as  in  the  analogous 
cases  of  anelectrotonus  and  blocking  at  a  region  of  injury. 

2  Keith  Lucas,  Conduction  of  tfie  Xenons  ImpiJsc,  diapi.  xu,  xui. 


398    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

successive  waves  of  innervation  are  received.  At  each 
stimulation  the  decrement  in  the  end-plate  is  increased 
temporarily.  According  to  the  degree  of  decrement 
an  impulse  received  by  the  end-plate  may  penetrate 
the  latter  and  reach  the  muscle  cell  with  its  normal 
'intensity,"  or  it  may  undergo  a  decrease  which  may 
entirely  prevent  penetration.  A  grading  of  the  intensity 
of  innervation,  depending  on  the  degree  of  coincidence 
of  phase  in  the  natural  rhythms  of  the  two  interconnected 
systems,  is  thus  possible.  Forbes  has  recently  applied 
this  conception  to  the  case  of  sensory  stimulation,  and 
has  expressed  the  view  "that  an  unlimited  range  of 
sensory  graduation  might  be  based  on  the  frequency  with 
which  the  impulses  follow  one  another  in  the  sensory 
fibers."^  All  of  these  possibiHties  should  be  fully  studied 
and  investigated,  with  a  recognition  of  the  probable 
dependence  of  excitation  and  transmission  upon  the 
bioelectric  processes  in  the  irritable  elements.  Further 
discussion  of  this  problem  is  not  possible  in  this  place.'' 
The  role  of  the  bioelectric  currents  in  other  physi- 
ological processes  (growth,  cell-division,  secretion,  etc.) 
is  only  beginning  to  be  understood,  and  much  further 
investigation  is  required.  It  seems  clear,  however,  that 
by  means  of  these  currents  physiological  influence 
may  be  transmitted  rapidly  to  a  distance  in  many 
protoplasmic  systems  other  than  nerve;  and  that 
correlations  of  activity  and  function  may  thus  be 
effected  which  would  otherwise  be  impossible.     Appar- 

*  Of.  Forbes,  Physiological  Reviews,  II  (1922),  361  (cf.  p.  388);  Forbes 
and  Gregg,  American  Journal  of  Physiology,  XXXIX  (1915),  172. 

'  See  Sherrington,  "Some  Aspects  of  Animal  Mechanism,"  Nature,  CX 
(1922),  346. 


PHYSICO-CHEMICAL  liASIS  OF  TRANSMISSION    399 

ently  this  general  condition  is  illustrated  in  the  phe- 
nomena of  growth  and  development.  There  is  evidence 
that  many  cases  of  form-correlation  in  both  j)lants  and 
animals  have  an  electrical  basis.  Actively  growing 
regions  of  organisms  have  usually  been  found  electrically 
negative  to  more  slowly  growing  regions.  Hermann  and 
Miiller-Hettlingen^  obser\'ed  that  in  seedlings  the 
regions  near  the  growing  zones  (terminal  buds  and  root- 
tips)  were  negative  to  those  near  the  cotyledons;  similarly 
the  growing  zones  of  planarians  and  annelids  are  negative 
to  intermediate  regions,''  and  in  hydroids  regenerating 
hydranth  heads  are  negative  to  the  stems. ^  In  general 
the  indications  are  that  regions  of  active  constructive 
metaboHsm — which  are  usually  regions  of  active  oxidation 
— are  t}T)ically  negative  to  less  active  regions.  Miss 
Hyde's  observations  on  fish  eggs^  indicate  that  during 
cell-division  the  cell  body  undergoes  a  temporary 
negative  variation,  analogous  to  that  accompanying 
excitation;  the  electrical  negativity  of  regions  in  active 
proKferation  may  thus  be  accounted  for. 

The  presence  of  bioelectric  circuits  between  the 
rapidly  growing  regions  of  an  organism  and  the  regions 
adjoining  is  in  all  probability  an  important  if  not  the 
chief  factor  in  the  controlling  influence  (''physiological 
dominance")  which  the  former  exerts  upon  the  Hitter. 
In  plants  it  has  long  been  known  that  the  removal  of 

» Hermann,  Arch.  ges.  Physiol.,  XXVH  (1882),  28S;  MuUcr- 
Hettlingen,  ibid.,  XXXI  (1883),  193- 

^Cf.  Child,  Biological  Bulletin,  XLI  (1921),  90;  H>'inan  and 
Bellamy,  ibid.,  XLIII  (1922),  313. 

3  Mathews,  American  Journal  of  Physiology,  VIII  (1903),  394; 
Lund,  Journal  of  Expcrijncntal  Zoology,  XXXVI  (19-^^),  477- 

4 1.  H.  Hyde,  American  Journal  of  Physiology,  XI  (1904)1  5  J- 


400    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

growing  regions  (terminal  buds)  initiates  growth  in  the 
dormant  regions  adjacent  (axillary  buds,  etc.);  any 
arrest  of  growth  by  cold,  anaesthetization,  or  removal 
of  oxygen  has  the  same  effect.^  Such  facts  show  that 
pronounced  activity  of  growth-processes  in  one  region  in 
some  manner  involves  repression  of  similar  processes 
in  neighboring  regions;  and  this  effect  has  been  shown 
in  certain  cases  to  be  independent  of  the  transport  of 
special  growth-inhibiting  substances  between  the  two 
regions.^  A  similar  inhibitory  influence  of  one  embryonic 
area  on  another  is  seen  also  in  the  development  of 
animals.  3 

The  hypothesis  that  the  essential  basis  of  this  growth- 
controlling  influence  is  electrical  is  consistent  with  the 
observation  that  in  certain  organisms  the  rate  and  direc- 
tion of  grow^th  can  be  experimentally  controlled  by 
electric  currents.  We  have  seen  that  in  hydroid  stems 
the  growing  or  regenerating  hydranths  are  negative 
relatively  to  other  regions  of  the  stem  and  to  the  stolons. 
Apparently,  therefore,  a  normal  accompaniment  of 
growth  is  the  passage  of  electric  currents  in  a  constant 
direction  through  the  organism;  and  the  direction  of 
the  current  through  the  galvanometer  shows  that  the 
positive  stream  enters  the  living  system  (from  the 
exterior)  at  the  regions  where  growth  is  most  rapid. 
If  electric  currents  are  in  themselves  a  factor  in  the 

^McCallum,  "Regeneration  in  Plants,"  Bot.  Gaz.,  XL  (1905),  97, 
241. 

2  Child  and  Bellamy,  Science,  L  (1919),  362;  Bot.  Gaz.,  LXX  (1920), 
249;  Harvey,  America^i  Naturalist,  LIV  (1920),  362. 

3  Cf.  Stockard,  American  Journal  of  Anatomy,  XXVIII  (192 1), 
115- 


PHYSICO-CHEMICAL  BASIS  OF  TRANSMISSION    401 

growth  process,  it  is  to  be  expected  lliat  their  passage 
through  the  organism  from  without  should  either 
promote  or  inhibit  growth  according  to  the  direction  of 
flow.  Lund  has  in  fact  recently  shown  that  the  regenera- 
tion of  new  polyps  from  the  cut  stems  of  the  hydroid 
Obelia  may  be  controlled  by  weak  electric  currents 
passed  lengthw^ise  through  the  stems;'  the  formation  of 
hydranths  is  promoted  where  the  current  passes  so  as 
to  enter  the  protoplasm  from  the  medium — i.e.,  at  the 
cut  end  facing  the  positive  pole  of  the  battery  -and 
inhibited  at  the  other  end.  The  normal  polarity  of  a 
stem  can  thus  be  reversed  by  passing  the  current,  a 
result  in  agreement  with  the  view  previously  exi)ressed 
by  Mathews  that  morphological  polarity  in  these 
organisms  has  an  electrical  basis.^  Bose  has  also  found 
that  the  electric  current  influences  growth  processes  in 
the  higher  plants  in  a  polar  manner,  the  anode  enhancing 
and  the  cathode  depressing  the  normal  rate.^  Recently 
Ing\^ar  has  reported  experiments  in  which  the  outgrowth 
of  processes  from  embryonic  nerve  cells  is  influenced  in  a 
directive  manner  by  the  passage  of  weak  currents 
through  the  culture  medium.  Here  also  a  polar  influence 
is  seen,  the  processes  growing  toward  the  anode  dilTering 
morphologically  from  those  growing  toward  the  cathode* 
All  of  these  facts  show  clearly  that  growth  j)rocesses 
resemble  the  processes  of  stimulation  in  irritable  tissues 
in  being  subject  to  electrical  control;  further  that  in  this 

^  Lund,  Journal  oj  Experimental  Zoology,  XXXI \'  (igii),  471. 
"  Mathews,  loc.  ciL 

3  Bose,  Proceeding's  of  the  Royal  Society,  li,  XC  (1918),  364. 

4  Ingvar,   Proceedings  of  the  Society  of  Experimaital  Biology  and 
Medicine,  XVII  (1920),  198. 


402    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

control  the  polar  influence  is  all-important/  If  what  is 
true  of  artificial  electric  currents  is  true  also  of  the 
currents  produced  by  the  Kving  system  in  its  own 
activity,  the  conclusion  seems  unavoidable  that  the 
bioelectric  currents  exert  a  controlHng  and  co-ordinating 
influence  in  normal  growth  processes  as  well  as  in  normal 
stimulation.^ 

Perhaps  the  most  important  general  inference  to  be 
drawn  from  such  experiments  is  that  the  electric  current 
under  appropriate  conditions  has  a  direct  promoting 
influence  on  the  synthetic  reactions  in  living  matter, 
i.e.,  those  underlying  growth  and  repair,  as  well  as  on 
the  reactions  involving  oxidation  and  decomposition 
which  yield  the  energy  for  normal  activity.  Many 
years  ago,  before  the  development  of  modern  physical 
chemistry,  Hering  reached  certain  general  conceptions  of 
the  relation  of  the  current  to  protoplasmic  action 
resembhng  closely  in  many  respects  those  reached  as  the 
result  of  our  present  analysis.^  Hering  regards  the 
bioelectric  currents  as  essentially  an  index  of  chemical 

'  In  a  recent  paper,  I  have  called  attention  to  a  number  of  analogies 
between  organic  growth  and  the  growth  of  precipitation-structures  on 
metals  (Zn,  Fe,  Co,  etc.)  in  ferricyanide  solutions;  control  by  electrical 
conditions  is  also  characteristic  of  such  precipitation-growths  (Biological' 
Bulletin  [1917],  loc.  cit.;  cf.  pp.  162  ff.). 

*  According  to  Kappers,  the  direction  of  outgrowth  of  nerve-tracts 
in  the  central  nervous  system  is  the  expression  of  a  directive  electrical 
influence  (analogous  to  galvanotropism)  which  he  calls  "neurobiotaxis." 
Cf.  Kappers,  "On  Structural  Laws  in  the  Nervous  System,"  Brain^ 
XLIV  (1921),  125,  and  earlier  references  there  given.  Cf.  also  Child's 
discussion  in  his  Origin  and  Development  of  the  Nervous  System,  University 
of  Chicago  Press  (1921),  chaps,  x,  xi. 

3  Hering,  Lotos,  IX,  Prag  (1888),  translated  in  Brain,  XX  (1897), 
232. 


PHYSICO-CHEJVIICAL  BASIS  OF  TRANSMISSION    403 

reactions  occurring  in  the  protoplasm;  conversely, 
electric  currents  passing  through  protoplasm  from  with- 
out alter  its  activity  through  their  direct  intlucncc  on  its 
chemical  processes.  Hering  also  concludes,  from  the 
contrast  between  the  physiological  elTects  at  the  two 
electrodes,  that  where  the  current  enters  protoplasm 
from  the  surroundings  it  induces  or  promotes  (7jji;;;/7(//f>ry 
(anabolic)  processes,  and  where  it  leaves,  dissimilalorv 
(catabolic)  processes.  In  the  typical  irritable  tissue  the 
inhibitory  effect  at  the  anode  is  the  expression  of  a 
predominance  of  anabolic  processes,  while  the  stimulation 
at  the  cathode  results  from  chemical  effects  of  the  reverse 
kind  (predominantly  catabolic). 

From  our  present  point  of  view  the  above-described 
influences  on  growth  and  regeneration  point  to  the  conclu- 
sion that  where  the  current  enters  the  protoplasmic  sur- 
face from  the  exterior  it  has  the  efTect  of  promoting 
oxidation  processes  w^hich  form  secondarily  the  condition 
of  the  syntheses  required  for  the  formation  of  new  struc- 
ture. Growth,  repair,  and  recovery  from  stimulation  are 
the  result  or  expression  of  cliemical  reactions  of  the  same 
general  kind,  apparently  oxidative  syntheses,  which  occur 
predominantly  at  the  one  polar  region.  At  the  other 
polar  region  reactions  of  the  reverse  kind  are  promoted; 
these  form  the  condition  for  stimulation  in  irritable 
tissues  or  for  cessation  of  growth  or  regression  in  growini: 

regions. 

The  closest  physico-chemical  analogies  to  >uch 
processes  are  furnished  by  the  chemical  etlects  at  elec- 
trodes, i.e.,  the  phenomena  of  electrolysis;  and  the  possi- 
bility that  electrolysis  may  underlie  the  i)hysiological 
effects  of  the  electric  current  was  in  fact  carlv  recoLMii/.ol 


404  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

by  Du  Bois-Reymond  and  other  physiologists.^  Evi- 
dently the  fundamental  problem  to  be  solved  is  the 
problem  of  the  physico-chemical  basis  of  electrical 
sensitivity  in  living  matter.  The  various  facts  and 
considerations  reviewed  in  the  foregoing  chapters  indicate 
that  this  basis  is  to  be  found  in  the  characteristic  physical 
structure  of  protoplasm;  in  other  words,  that  the 
polyphasic  and  film-partitioned  feature  of  the  system 
is  the  condition  which  makes  it  possible  for  the  electric 
current  to  produce  such  definite  chemical  effects.  The 
polar  action  of  the  current  is  a  clear  analogy  to  electrode 
action,  and  "vve  have  to  inquire  into  the  justification  of 
regarding  the  protoplasmic  surfaces  as  having  properties 
like  those  of  electrode  surfaces  in  general.  At  the  surface 
of  a  metallic  electrode,  chemical  action  occurs  when  the 
current  passes  between  metal  and  solution;  and  appar- 
ently the  same  occurs  when  a  current  passes  from  one 
protoplasmic  phase  to  another;  e.g.,  during  electrical 
stimulation  from  the  surface  of  the  plasma  membrane 
to  the  adjoining  medium.  As  we  have  seen,  the  passage 
of  the  current  (positive  stream)  in  this  direction  is  the 
condition  of  stimulation  in  an  irritable  cell  or  nerve 
fiber. 

The  parallels  between  the  surface  of  a  metallic 
electrode  and  the  surface  of  a  living  cell  or  organic 
membrane  have  already  been  discussed  in  part,  and 
certain  resemblances  have  been  pointed  out.  It  remains 
to  be  seen  whether  the  two  are  similar  in  the  further 
respect  that  the  passage  of  an  electric  current  across 

^  Cf.  Du  Bois-Re>Tnond,  Untersuchungen  iiher  tierische  Elektricitdt, 
II,  387  (" galv^anische  Reizung  ist  uns  nichts  mehr  als  die  erste  Stufe 
der  Elektrolyse  eines  Nerven"), 


PHYSICO-CHE.MICAL  BASIS  OF  TRANSMISSION'    405 

the  surface  is  in  both  cases  attended  with  chemical 
change.  The  chief  peculiarity  of  the  chemical  reactions 
occurring  under  the  inlluence  of  electric  currents  in 
electro-chemical  circuits  is  that  they  are  confined  to  the 
boundary  region,  where  the  current  passes  between  the 
electrode  and  the  electrolyte  solution.  Xo  chemical 
change  occurs  in  the  interior  of  either  ])hase;  the  reactions 
are  surface  reactions.  Since  the  region  of  transition  from 
the  metallic  conductor  to  the  electrolytic  conductor  is 
the  only  region  in  the  circuit  where  the  passage  of  the 
current  involves  chemical  change,  the  fundamental 
question  relates  to  the  general  ])hysical  nature  of  the 
conditions  in  this  region  while  the  current  is  llowing. 
According  to  modern  i)hysico-chemical  theory,  the 
carriers  of  the  current  in  the  electrolyte  solution  arc  the 
anions  and  cations  of  the  dissociated  electrolyte;  in  the 
metal  the  carriers  are  free  electrons.  At  the  surface  of 
contact  there  is  a  transfer  of  electrons  between  the 
electrode  and  the  ions  of  the  solution.  For  example,  at 
the  anode,  ferrous  ions  are  o.xidized  to  ferric  ions;  on 
the  electron  theory  this  implies  the  transfer  of  an  electron 
from  each  ferrous  ion  to  the  electrode;  conversely,  at  the 
cathode  electrons  are  transferred  from  the  metal  to  the 
ions  in  solution,  H  ions  becoming  uncharged  H  atoms. 
To  effect  tliis  transfer  a  certain  })otential  gradient  is 
required;  it  would  appear  therefore  that  the  region  of 
transition  represents  that  portion  of  the  circuit  where  the 
potential  gradient  is  steepest  and  where  the  forces  acting 
to  displace  electrons  are  greatest.  That  the  contact 
of  two  dissimilar  conductors,  respectively  metallic  and 
electrolytic,  is  not  the  essential  condition,  but  rather  the 
existence  of  a  large  fall  of  potential  across  a  short  distance, 


4o6    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

is  indicated  by  the  facts  of  electrostenolysis  and  by  the 
chemical  effects  produced  by  intense  electrical  discharges 
(sparking,  etc.). 

The  general  fact  that  chemical  effects  are  produced 
in  protoplasm  by  the  electric  current  and  that  protoplasm 
produces  electric  currents  in  its  activity,  when  considered 
in  conjunction  with  the  further  fact  that  these  phenomena 
are  dependent  on  the  structure  of  the  living  system  and 
disappear  with  the  loss  of  semi-permeabiHty  (as  at 
death) — as  well  as  the  various  other  facts  reviewed  above, 
which  relate  stimulation  to  membrane  changes — indicates 
clearly  that  the  electrical  sensitivity  of  hving  protoplasm 
is  intimately  connected  with  the  presence  of  the  semi- 
permeable partitions  or  surface-films.  These  partitions 
have  high  electrical  resistance  and  are  therefore  highly 
polarizable;  they  are  also  extremely  thin;  hence  when 
they  are  polarized  by  the  passage  of  a  current  there  is  a 
correspondingly  steep  fall  of  potential  between  their 
opposite  faces.  The  hypothesis  naturally  suggests  itself 
that  the  existence  of  these  steep  gradients  is  the  essential 
condition  on  which  the  chemical  action  of  the  electric 
current  in  living  protoplasm  depends. 

We  have  recently  attempted  to  put  this  hypothesis 
to  an  experimental  test  by  passing  electric  currehts 
through  electrolyte  solutions  partitioned  by  artificial 
membranes,  combining  extreme  thinness  with  high  elec- 
trical resistance.'  Such  a  membrane,  consisting  of  a  thin 
film  of  rubber  or  other  insoluble  non-conducting  material 

^  R.  S.  Lillie  and  S.  E.  Pond,  "  Chemical  Effects  Produced  by  Passing 
Electric  Currents  through  Thin  Artificial  Membranes  of  High  Electrical 
Resistance,"  American  Journal  of  Physiology  (1923);  Proceedings  of  the 
Ajuerican  Physiological  Society,  December  (1922). 


PHYSICO-CHEMICAL  BASIS  OF  TRAXSMISSION    407 

supported  in  a  sheet  of  lens  i)ai)cr,  is  intcn)()sc(I  between 
two  salt  solutions,  one  of  wliich  contains  a  readily 
oxidizable  compound,  ferrous  chloride,  together  with  an 
indicator  (KCNS)  to  show  the  formation  of  ferric  ions. 
With  membranes  of  about  sofi  thickness  and  a  P.O.  of 
about  II  volts  between  the  two  faces,  the  red  color  of 
ferric  thiocyanate  appears  rai)idly  at  the  surface  facing 
the  cathode;  i.e.,  where  the  positive  stream  of  the 
current  passes  from  the  membrane  to  the  solution.  The 
surface  of  the  membrane  under  these  conditions  acts 
(in  the  quaUtative  sense)  like  the  surface  of  a  platinum 
anode.  When  the  direction  of  the  current  is  reversed, 
ferric  ions  are  reduced  to  the  ferrous  state,  as  shown  by 
the  gradual  disappearance  of  the  color.  In  order  to 
obtain  these  electrolysis-like  effects,  a  certain  minimal 
P.D.  (i.e.,  steepness  of  gradient)  across  the  membrane  is 
required;^    for  example,  with  a  current  giving  9  volts 

*  There  is  an  interesting  analogy  here  with  the  conditions  of  clcctro- 
stenolysis,  where  also  a  critical  P.D.  is  required  for  pro<lucinK  chemical 
effects.  In  the  experiments  of  Braun  (Ann.  d.  Physik,  XLIV  (1891), 
N.F.,  473)  thin  sheets  of  mica  were  used  (ca  8o/x  thick)  in  which  fissures 
were  cut;  metallic  silver  separates  out  rapidly  at  the  borders  of  the  fissure 
when  a  strong  current  is  passed  through  such  a  sheet  separating  two 
solutions  of  AgNGj.  Braun  compares  such  chcmic;il  ciTccts  with  Bcc- 
querel's  "electrocapillary  reactions"  (of.  Comptcs  rend  us,  LXW'I 
[1873],  1037)  ^^d  suggests  tliat  tliey  may  have  biological  significance; 
he  regards  a  narrow  split  or  fissure  in  a  thin  layer  of  insulating  material 
as.  acting  essentially  like  an  electrode;  a  certain  critical  intensity  of 
current  is  required,  below  which  tliere  is  no  sejxiralion  of  mcUil.  Acros^s 
the  fissure  there  is  a  steep  fall  of  potential,  whicii  he  estimates  at  700-900 
volts  per  millimeter  in  currents  efTective  with  AgXGj. 

For  observations  on  chemical  effects  at  preci[)ilalion  membranes 
through  which  electric  currents  are  passed  cf.  Ostwald,  Z.  physik.  Chcm., 
VI  (1890),  71;  Overbcck,  Ann.  d.  Physik,  XLII  (1891),  193;  SprinR- 
mann,  ibid.,  LI  (1894),  140;    Bein,  Z.  physik.  Chew.,  XXVIII  (1SQ9), 

439- 


4o8    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

P.D.  across  the  membrane,  no  effect  is  obtained  in  half 
an  hour  or  more.  The  effective  gradient  of  about  lo 
volts,  across  a  partition  50  /x  thick,  is  equivalent  to  a 
fall  of  about  2,000  volts  per  centimeter. 

From  these  experiments  we  may  conclude  that  an 
arrangement  of  electrolyte  solutions  containing  oxidizable 
materials  and  partitioned  by  thin  films  of  water-insoluble 
material  having  high  electrical  resistance  will  be  the 
seat  of  chemical  change  (oxidations  and  reductions) 
occurring  at  the  surface  of  the  partitions  when  the  system 
is  traversed  by  an  electric  current  of  sufficient  intensity. 
It  seems  probable  that  this  kind  of  structural  arrange- 
ment is  the  one  upon  w^hich  the  electrical  sensitivity  of 
living  matter  depends.  We  have  already  seen  that  this 
type  of  structure  is  characteristic  of  living  protoplasm. 
The  potentials  in  protoplasm  are  much  smaller  than 
those  used  in  the  experiment  above;  apparently  50  to 
100  millivolts  is  the  usual  order  of  the  variations  of 
potential  in  the  bioelectric  processes;  but  the  proto- 
plasmic films  are  much  thinner  than  those  used  in  our 
model;  and  since  the  steepness  of  the  gradients  rather 
than  the  absolute  values  of  the  potentials  is  the  essential 
factor  to  be  considered,  the  conclusion  seems  justified 
that  conditions  similar  to  the  above  exist  in  Hving 
protoplasm  when  the  system  is  traversed  by  a  current. 

The  parallel  between  the  passive  iron  system  and  an 
irritable  protoplasmic  system  such  as  a  nerve  axone  may 
be  described  in  general  terms  as  follows.  In  both  cases 
there  are  two  electrically  conducting  phases  separated 
by  a  thin  impermeable  film  of  chemically  alterable 
material.  In  protoplasm  both  of  the  phases  are  electro- 
lytic conductors.     In  the  passive  iron  system  only  one 


PHYSICO-CHEMICAL  BASIS  OF  TRANSMISSiuN     40Q 

phase  is  electrolytic,  the  other  bcinp^  metallic;  hut  the 
chemical  reaction,  which  is  confined  to  the  intcrfacial 
layer,  does  not  depend  directly  on  the  internal  composi- 
tion and  physical  properties  of  either  i)hase  but  only 
upon  the  conditions  at  the  interface.  When  a  current 
of  sufficient  intensity  passes  across  the  boundary  at  any 
region,  in  either  system,  it  causes  polarization  and  pro- 
duces chemical  effects;  and  under  the  conditions  already 
defined,  these  effects  may  be  automatically  transmitted 
over  the  whole  surface. 

Such  a  conception  of  protoplasmic  structure  and 
action  is  fully  consistent  with  the  views  reached  on  the 
basis  of  histological  research,  and  it  has  the  further 
advantage  of  correlating  the  structural  features  of  the 
living  system  with  the  special  peculiarities  of  its  chemical 
and  physiological  behavior.  The  great  di\ersity  exhib- 
ited by  living  organisms  shows  that  the  protoplasmic 
type  of  constitution  permits  the  widest  variation  in  the 
details  of  structure  and  activity,  ^'ct  the  essential  or 
fundamental  structure  common  to  all  forms  of  j)r()toplasm 
is  apparently  uniform;  viz.,  a  film-partitioned  or  film- 
bounded  arrangement  or  organization  of  phases  of  dilTcr- 
ent  chemical  composition.  With  this  type  of  structure, 
of  which  an  elementary  model  is  an  emulsion  structure, 
the  properties  of  growth,  chemical  activity,  and  irrita- 
bihty  characteristic  of  living  matter  api)ear  to  be  inti- 
mately bound  up.  Systems  having  this  structure  will 
give  a  maximum  of  polarization  when  traversed  by 
electric  currents,  and  hence  a  ma.ximum  of  chemical 
effect.  Most  of  the  problems  relating  to  the  mode  of 
action  of  such  systems,  especially  the  problem  of  the 
conditions  of  specific  synthesis  (the  most  charartrristic 


410    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 

property  of  living  matter),  are  still  unsolved.  The 
study  of  artificial  systems  having  a  similar  type  of 
physical  constitution  may  be  expected  to  throw  further 
light  on  the  nature  of  protoplasmic  action,  and  also  to 
indicate  the  directions  in  which  further  physiological 
research  is  most  desirable. 


INDEX 


PROPERTY  UBRART 
]I  C.  State  College 


Absorption,  94,  102,  no 

Action  currents,  311  fif.  See  Bio- 
electric variations 

Activation,  changes  of  permea- 
bility and,  353  il.;  of  egg  cells, 
74,  265,  353  ff.;  of  passive  iron, 
254;  by  salt  solutions,  351 

Adaptation,  2,  8,  9,  30;  active,  9, 
30;  static,  9 

Adsorption,  23,  63,  75  fT.;  catalysis 
and,  76,  83,  91,  239  ff.;  chemical 
reactions  and,  83,  90;  electrical 
factors  in,  84;  films,  58;  irre- 
versible, 76,  77,  82;  narcotic 
action  and,  96,  201  ff.,  233; 
potentials,  88,  93,  300;  selective, 
79;   specific,  78,  79,  82 

Agglutination,  163,  208 

"All  or  none"  reactions,  324,  386 

Alternating  currents,  activation 
by,  257;  stimulating  action  of, 
278,357 

Anaesthesia  {see  also  Narcosis), 
40,  42,  47,  83,  142,  189  ff., 
263;  by  electric  current  {see 
Electrotonus) ;  relation  to  per- 
meability, 353,  363 

Anaphylaxis,  35,  266,  370 

Animals  and  plants,  12,  28 

Antagonisms,  by  salts,  155,  157, 
158,  164  ff.,  176,  181  ff.,  351; 
between  salts  and  anesthetics, 
211,  352 

Anticatalysis,  202,  226  ff.,  236 

Antigenic  properties,  relation  to 
specificity,  34,  35,  36,  37 

Antito.xic  action,  of  salts,  164  ff.; 
of  anaesthetics,  211,  352 

Asymmetr>',  chemical,   specificity 

and, 34 
Autocatalysis,  36 

Autolysis,  44,  48,  56,  57,  377 


Bacteria,  14 

Bioelectric   potentials,   membrane 
theories  of,  302  ff.;    r  '     '       to 
permeability     of      nuw. 
301  ff.,  311  ff.;    resting,   . 
variations  with  activity,  311  li. 

Bioelectric  variations,  311  ff.; 
range,  324;  rate  in  relation  to 
physiological  proccs>ts,  320,  321, 
322,  326  ff.;  relation  to  trans- 
mission, 322,  330,  387  ff; 
rhythm  of,  330  ff. 

Bioluminescence,  375 

Blood  corpuscles,  isoelectric  point 
of,  100 

Calcium  salts,  45,  iiq,  ?55  ff.; 
antitoxic  or  stabilizing  action, 
351  ff,,  369;  inCuence  on  per- 
meability, 119;  relation  to 
excitation  processes,  290;  sum- 
mation-interval and,  292 

Capillarity,  77 

Catalysis,  62,  63,  202.  217  ff., 
223,  226  ff.;  adsorption  ami. 
223  ff.,  239  ff.;  by  charc^ul, 
243,  245;  contact,  2i6,  222  ff., 
243  ff.;  electric  factors  in,  245, 
246  ff.;  influence  of  surface- 
active  compounds  on,  220  ff.; 
by  platinum,  237,  245;  rhythmi- 
cal, 63,  247  ff.,  2gS;  r6ic  of 
surface-films  in,  247  ff. 

Cataphorcsis,  91,  99,  300 

Cell,  14,  15  ff.,  67,  98,  108; 
division,  316,  356,  363 

Cell-division,  316,  356,  363;  elec- 
trical variation  during,  364,  398, 
399 

Chemical  reactions,  rhytJjmir.n!. 
247,  250 

Chemical  sensitivity,  46,  47,  2OO 

Chromosomes,  6,  7 


411 


412    PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 


Chronaxia,  275  ff.,  287  ff.,  326, 
327;  relation  to  refractory 
period,  338 

Cilia,  59,  165 

Circuits,  bioelectric,  as  factors  in 
transmission,  382  ff.;  local,  63, 
221,  236,  260,  271,  274 

Colloids,  68,  69,  81,  85  ff. 

Compensation,  of  bioelectric  cur- 
rents in  protoplasm,  397 

Conduction,  of  excitation,  etc. 
See  Transmission 

Conductivity,  electrical,  of  artifi- 
cial membranes,  179;  of  cell- 
interior,  122  ff.;  changes  during 
activation  or  stimulation,  356, 
361;  of  living  cells,  118,  119, 
122  ff.,  130,  358,  359;  of 
medium   in    relation    to    trans- 

\  mission,  390  ff. 

Contact  potentials,  236  ff. 

Contractile  processes,  59,  60,  378 

Convection,  electrical,  of  cells,  91, 
99,  300 

Core-conductors,  380,  390 

Correlation,  11,  of  growth,  41,  42, 

399  ^^ 
Cortical     reaction,     of     egg-cells, 

360,  362 

Crystal  forms,  32,  z2>,  34 
Crystallization,  relation  to  growth, 

79,  225 
Ctenophore,    swimming  plate   of, 

45,  59,  60,  367 
Cyclopia,  39,  40 
Cytolysis,  58,  74, 166,  199,  208,  355 

Cytolytic  agents,  57,  59;  activa- 
tion by,  355;  stimulation  by, 
351  ff.,  366,  367 

Cytoplasm,  relations  between 
nucleus  and,  17 

Death  process,  48,  54,  56,  58,  59,  64 
Decrement,     transmission     with, 

397,  398 
Demarcation       potentials,       160, 

306  ff. 


Depolarization,  relation  to  stimu- 
lation, 283,  284 

Development,  6,  7,  62;  experi- 
mental control  of,  38,  39,  40 

Diffusion,  21,  48,  57,  102;  as 
factor  in  electrical  stimulation, 
279,  294;  potentials,303,307,3i9 

Disintegration,  polar,  277,  360 
Distance-action,     chemical,     260, 
393;    physiological,  393,  398  ff. 
Dominance,  physiological,  399 

Egg-cells,  changes  of  permeability 
during  activation,  360  ff . 

Electric  organs,  317 

Electrical  activation,  of  passive 
iron,  254,  255 

Electrical  conductivity,  of  artifi- 
cial membranes,  179;  of  cells, 
118,  119,  122  ff.,  130,  358, 
359;  of  cells  during  activation 
or  stimulation,  356,  361;  of 
external  medium  in  relation  to 
speed  of  transmission,  390  ff . 

Electrical  convection,  91,  99,  300 

Electrical  endosmose,  94,  147,  148, 
300,  301 

Electrical  sensitivity,  of  proto- 
plasm, 46,  47 

Electrical  stimulation,  273,  2745.; 
secondary,  388,  389,  392 

Electrocatalysis,  220,  236 

Electrode  potentials,  304 

Electrolysis,  63,  219,  220,  235  ff., 
252  ff.,  277,  282,  298,  403,  406; 
intermittent,  250;  as  factor  in 
transmission,  253,  382;  at  sur- 
face of  membranes,  407 

Electrolytic  oxidations  and  reduc- 
tions, 282 

Electrostatic  conditions,  in  nerve 
transmission,  390 

Electrostenolysis,  406,  407 

Electrotonic  currents,  358 

Electrotonus,  256,  277,  395  ff. 

Emulsions,  67,  68,  70  ff.,  98,  104, 
177 


INDKX 


413 


Environment,  relations  of  organ- 
isms to,  25  flf.;  as  source  of 
stimuli,  263 

Enzymes,  54,  56,  222  fT.,  240  tT.; 
specific  action  of,  224 

Equilibration,  10,  26 

Equilibrium,  vital,  4^,  40 

Excitation.     Sec  Stimulation 

Explosive  corpuscles,  270,  349 

Fatigue,  structural  changes  in,  Oi 
Fermentation,  alcoholic,  53,  226 

Films,  interfacial,  71,  72,  78,  go, 
98,  104,  105,  106,  177;  relation 
to  activation,  298;  relation  to 
rhythmical  chemical  action, 
247  fif- 

Films,  protoplasmic,  formation  of, 
126  ff.,  350 

Film-structure,  changes  during 
stimulation,  346  IT.;  importance 
in  protoplasm,  60,  loi,  104,  i^O, 
127,  128 

Foam  structure,  70,  71,  74 

Form-correlation,  399 

Form-determination,  32 

Formative  metabolism,  65 

Fuse,  transmission  in,  384 

Galvanotropism,  277 
Gelation,  by  narcotics,  228,  229 
Gels,  70,  106,  107 
Genes,  6,  7 

Growth,  2,  4,  5,  36,  38,  42,  79; 
action  of  narcotics  on,  42; 
bioelectric  phenomena  of,  39S, 
399;  crystalline,  79,  225;  de- 
pendence on  oxidations,  403; 
dependence  on  specific  synthesis. 
42  ff.,  54,  217;  polar  inliuencc  of 
electric  current  on,  401;  rela- 
tions to  normal  physiological 
activity,  41  ^■ 

Haemogloljin,  crystal  forms  of,  a 
Haemolysis,  99,  163,  iQQ,  -O'*^.  21.^ 
Heat-production,  50 


Heredity,  2,  4,  5,  .-,  .,.  ,  .  v^. 
factors  of,  38,  39;  rclatidn  lr» 
growth,  4,  27,  38 

Homologous  scries,  physiologic  a! 
action  of,  1 1 1,  197 

Hormones,  as  factors  in  integra- 
tion, 7,  1 1 

Hydrogen   ion  concentration,  85, 

88,  89,  93 
Hydrolysis,  48,  Si 

Inhibition,  45,  59,  62,  304.  ?07; 
of  growth,  400 

Injury  currents,  209;   influence  of 

aniusthetics  on,  309 
Inorganic       salts,       physiological 

action  of,  151  ff.     See  Salts 

Instincts,  10,  11 
Integration,  9,  10,  11,  259 
Interfaces,  protoplasmic,  217,  26^^; 

relation  to  chemical  reactions  in 

cell,  217  fl.     Sir  Films 
Interference,  of  cxcitation-wavcs. 

396  a. 

Ions,  physiological  action  of, 
151  fl.     Sec  Salts 

Ion-antagonisms,  92,  155  f^-  ^^^ 
Salts 

Iron,  passive,  activation  of,  254, 
255;  recover)'  of  lransmis>i\  ity 
in,  345,  346;  summation  ilTuls 
in,  255;  transmission  in.  -'53  ll., 
260,  270  fT.,  273,  298,  314. 
385  fT.,  396,  408 

Irritability,  2,  8,  30.  40,  43.  4t>. 
192;   relation  of  salts  to,  153  ff. 

Isocapillary  solutions,  198  ff. 
Isoelectric  point,  85,  So.   o^.  00. 
100;  of  cv\U.  100 

Kernleitcr  tlRut>  ,  380  ff. 

Lecithin,  properties  of  susj>cn 

228  IT. 
Light,  stimulation  by,  2(»0 
Liirht-pHHluction,    by    organism*, 

relation  to  vtinuil.itinn.  ;-; 


414   PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 


Lipoids,  presence  in  protoplasmic 
films,  184  ff.;  as  protoplasmic 
constituents,  58,  67,  in,  1845.; 
relation  to  narcosis,  83,  189  ff., 
214;  relation  to  permeability, 
iiiff. 

Lipoid-alterant  compounds,  action 
of,  56,  58,  III,  187  ff. 

Lipoid-solubility,  relation  to  physi- 
ological action  of  compounds, 
189  ff. 

Lithium  salts,  as  substitutes  for 
Na-salts,  40,  154,  161 

Living  matter,  general  characters 
of,  I  ff. 

Local  action,  382 

Local  circuits,  236,  245,  246,  250, 
253;  in  rhythmical  catah^sis, 
250;  in  transmission  in  passive 
iron,  253 

Local  currents,  role  in  transmis- 
sion, 386  ft\ 

Maintenance,  2,  3,  65 

Membrane  potentials,  107,  306  ff. 

Membrane  theory,  of  bioelectric 
potentials,  302  ff. 

Membranes,  artificial,  143  ff.,  185; 
electrical   conductivity   of,    179 

Membranes,  changes  during  stimu- 
lation, 207  ff.,  297,  302,  337  ff.; 
346  ff.;  electrical  polarization 
of,  159,  301  ff.;  permeability  of, 
109  ff.,  132  ff.;  plasma,  20,  21, 
22,  56,  57,  98  ff,  loi  ff.,_  109  ff., 
159,  160,  170;  stabilization 
during  narcosis,  207  ff.;  struc- 
ture, 180.     See  Films 

Membranes,  haptogen,  105;  por- 
celaine,  137;   precipitation,  136 

Mercury,  catalytic  action  of,  247 

Metabolism,  electrical  factors  in, 
402,  403;  formative,  7;  general 
role  in  living  matter,  2,  3,  4, 
25  ff.,  42  ff;  relation  to  proto- 
plasmic structure,  51  ff.,  63; 
synthetic,  relation  to  carbo- 
hydrate metabolism,  54 


Microdissection,  64,  128 

Muscle,  so,  55,  152  ff.,  162; 
contraction  of,  378;  smooth, 
172  ff. 

Myoneural  junctions,  156 

Narcosis,  189  ff.;  adsorption  and, 
196,  201  ff.,  233;  changes  in 
protoplasmic  viscosity  during, 
210;  decrease  of  permeability 
during,  209;  oxygen-consump- 
tion in,  195,  203  ff.;  partition- 
coefficients  and,  190  ff.;  temper- 
ature and,  193  ff.;  physical 
changes  in  protoplasm  during, 
206  ff.;  surface-activity  and, 
196  ff. 

Negative  osmosis,  147,  148 

Nerv^e,  261,  270;  bioelectric  varia- 
tions of,  328  ff.;  changes  of 
permeability  during  activity, 
357  ff.;  demarcation  potential 
of,  303ff.;  electrical  stimulation 
of,  267  ff.;  electrotonic  currents 
of,  358;  refractory  period  of, 
339  ff . ;  relation  of  salts  to 
irritabilit}^  of ,  155;  transmission, 

379  ff- 
Nerve  cells,   rhythmical   activity 
of,  332;    structural  changes  in 
death,  64 

Nerve  end-plates,  272,  287 

Nervous  impulse,  379  ff. 

Ner\^ous  system,  directive  factors 
in  growth  of,  402;  integrative 
action  of,  11;  neurone  theor}^  of, 

272 

Neurones,  272 

Non-electrolytes,  physiological 
effects  of  solutions  of,  151  ff. 

Nutrition,  2,  3,  6,  12 

Organisms,  general  characters  of, 
I,  2,  25  ff.,  49 

Organization,  chemical,  as  depend- 
ent on  film-partitioned  structure 
of  protoplasm,  22 

Oxidases,  376 

Oxidations,  electrolytic,  237,  246 


INDEX 


415 


Oxidations,  protoplasmic,  48,  50, 
5i»  53 J  55)  relation  to  structure, 
55,  206  n.;  relation  to  synthesis, 
growth,  recovery,  etc.,  403 

Oxygen-consumption,  influence  of 
narcotics  on,  195,  203  17.;  influ- 
ence of  salts  on,  iiS 

Parthenogenesis,  artificial,  352  fl. 
Partition-coefficients,    relation    to 

narcotic  action,  83,  190  ff. 
Partition  method,  of  determining 

permeability,  115 

Passivity    in    metals,     254.     Sec 

Iron,  passive 
Permeability,  loi  ff.,  132  ft.; 
changes  in  relation  to  stimula- 
tion and  activation,  207  fl.,  297, 
302,  337  ff-,  346  ff.;  electrical 
conditions  in,  146  ff.;  factors  in, 
133;  influence  of  narcotics  on, 
207,  209;  influence  of  salts  on, 
1 74  S. ;  methods  of  determining, 
112  ff.;  physiological,  103,  no, 
134;  of  plasma  membranes, 
106  ff.,  132  ff.,  154,  163,  171, 
178  ff.;  relation  of  chemical 
composition  to,  143  ff-;  relation 
of  structure  to,  135  ff. 

Phase-boundaries,  22,  23;  cata- 
lytic effects  at,  244;  proto- 
plasmic, 192,  196 

Phase-relations,  in  emulsions,  re- 
versal of,  178,  179 

Photocatalysis,  235 

Physiology,  scope  of,  2 

Plasmolysis,  113,  114 

Platinum,  catalytic  action  of,  237, 

245 
Polar  disintegration,  277,  360 

Polar  secretion,  360 

Polar  stimulation,  383  ff. 

Polarity,  morphological,  electrical 
factors  in,  400  ff . 

Polarizability,  changes  of,  during 
stimulation,  357  ff-;  of  living 
protoplasm,  280,  357,  ?>5^\  rela- 
tion to  semi-permeability,  297 


Polarization,  electrical,  98,  101, 
i5(),  iSi,  274  fl.;  rclat!""  '" 
stimulation,  273,  278  fl., 

Polarization,    physiological, 

344,  381 
Polarization-currents,     280,     281, 

357 
Potassium  salts,  156  tT. 
Potential,  chemical,  219 

Potential,  electric,  219;  variations 
during  periodic  catalysis,  249  ff.; 
variations  during  tran-  '  '  n 
in  passive  iron,  253,  21.  ,,,-;; 
variations  in  living  cells.  See 
Bioelectric  \ariations 

Protective     action,     of     colloids, 

231  fl. 
Proteins,    relation    to    specificity, 

31  ff. 

Protoplasm,  electrical  sensitivity 
of,  46,  274  ff.;  general  charac- 
ters, I  ff.;  physical  characters 
of,  48  ff.;  reactivity  of,  44  ff-, 
259  ff.;  specific  synthesis  in, 
35  ff.;  structural  changes  during 
acti\ity  or  stimulation,  34S  ff.; 
structure  of,  19,  56,  57,  58, 
61  ff.,  66  ff. 

Radioactivity,  172 

Reactivity,  of  living  matter,  29, 
30,  43  ff.    Sec  Irrilabiliiy 

Receptors,  266 

Refractory  period,  127,  297, 
337  ff.;  influence  of  chemical 
conditions  on,  340;  in  plants, 
374;  relation  of  ni"  '"-'nc 
changes  to,  344,  395;    '  '^^ 

to  bioelectric  variation,  3 
temi>erature-coeflJcient,         ^>4i . 
time-relations,  340 

Regenenition,  5,  17,  -1^'  r-li'i"" 
to  nucleus,  1 7 

Regulation,   2,  9,    »o,   ^<> 

general   property   of   hlalionar> 
systems,  50 

Reprotluction,  2,  45 


41 6  PROTOPLASMIC  ACTION  AND  NERVOUS  ACTION 


Resistance,  electrical,  of  plasma 
membranes,  103,  118.  See  Con- 
ductivity 

Response,  general  features  of 
organic,  8;  inhibitory,  45 

Rhythm,  in  activity  of  living 
cells,  251,  331;  in  bioelectric 
phenomena,  330  ff.;  in  surface- 
reactions,  247,  250 

Salts,  inorganic,  action  of  pure 
solutions,  164  £f.;  action  on 
permeability,  119,  174  ff.,  351; 
antagonisms  between  salts  and 
anaesthetics,  211,  352;  antago- 
nistic action  of,  155,  157,  158, 
164  ff.,  176,^  181  ff.,  351; 
balanced  action,  1675.;  in 
cells,  117,  120  ff.,  160;  physi- 
ological action  of,  151  ff.;  sensi- 
tization by,  162,  3675.;  stimu- 
lation by,  166,  351  ff. 

Secondary  stimulation,  388,  389, 

392 
Secretion,  94,  140,  374 

Semi-permeability,  20,  57,  58, 
103,  109;  factors  in,  132,  302. 
See  Permeability 

Sensitivity,  chemical,  266;  light, 
266.     See  Irritability 

Sensitization,  by  salt-solutions, 
162,  3675.;  specific,  370.  See 
Anaphylaxis 

Soaps,  relation  to  protoplasmic 
structure,  58,  180,  185 

Specific  energies,  law  of,  267 

Specificity,  5,  30  ff.  See  Synthe- 
ses, specific 

Square  root  law,  279,  282,  286 

Stabilization,  of  protoplasmic 
structure,  207  ff.;  of  suspen- 
sions, 230,  231 

Stationary  systems,  48 

Stimulation,  bioelectric  variations 
in,  297,  312  ff.;  changes  of 
polarization  in,  275,  276  ff.,  294; 
chemical,  266;  dependence  on 
surface  changes,  269  ff.,  296  ff.; 


electrical,  46,  285  ff.;  general 
features,  8,  43  ff.,  50,  51,  60,  62, 
74,  259  ff.;  by  light,  266; 
mechanical,  271;  membrane 
changes  in,  207  ff.,  297,  302, 
337  ff.,  346  ff.  {see  Permea- 
bility); by  salts,  166;  summa- 
tion in,  277,  .291  ff.;  time- 
relations  of,  278  ff. 

Structure,  protoplasmic,  relation 
to  chemical  activity  of  li\'ing 
matter,  52  ff.,  63.  See  Proto- 
plasm 

Summation,     in      activation      of 
passive    iron,    255;     in  .  stimu- 
•   lation,  277,  291  ff. 

Surface-activity,  82,  90,  187; 
relation  to  contact  potentials, 
236  ff.;  relation  to  ph3'siologicai 
action,  187,  196  ff.,  217 

Surface-films.  See  Films,  inter- 
facial 

Surface-tension,  71,  72,  78,  90, 
178,  192,  198  ff.,  237,  238,  249 

Synapses,  272 

Synchronous  activity,  of  cells,  392 

Syntheses,  as  basis  of  growth  and 
development,  3,  4  ff.,  42  ff'.,  54, 
217;  dependence  on  proto- 
plasmic structure,  53,  54,  63; 
electrical  factors  in,  402;  rela- 
tion to  protoplasmic  interfaces, 
217,  218;  specific,  27,  30,  31, 
34  ff.,  42,  48,  53,  54,  63 

Temperature-coefficients,  44;  of 
bioelectric  variations,  316,  321, 
333  ff.;  of  demarcation  poten- 
tials, 319;  of  minimal  duration 
of  threshold  stimulus,  286,  292; 
of  summation-interval,  292;  of 
protoplasmic  transmissions,  341, 
342;  of  recovery  of  trans- 
missivity  in  passive  iron, 
346;  of  refractory  period,  292, 
341 

Transmission,  in  nerve  and  other 
protoplasmic  systems,  152, 
259  ff.,  267  ff.,  379  ff.;  in  passive 


INDEX 


417 


iron,  253  ff.,  260,  270  ff.,  2q8, 
382,  385;  in  plants,  374.  See 
Stimulation 

Trigger  action,  262 

Turgor,    changes    resulting    from 
stimulation,  372  ff. 

Ultra-filtration,  107,  135 
Ultramicroscopy,  58 
Ultraviolet    rays,    activation    by, 
355,  363 


\'alcnce,  factor  in  physical  action 
of  ions,  (;i,  c)2,  03;  factor  in 
physiological  action  of  ions,  o-\ 
167  fT.,  175 

\'isua!  purple,  266 

X'italism,  2 

Vitamines,  260  n. 

Water-immiscibility,  of  proto- 
plasm, 22,  57 

Veast,  27 


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